I've done a little digging and found plenty of threads on other forums, but couldn't find anything relevant to my issues on D&DBeyond, so I'm risking a new post in the place with the most clout. I've been expecting the next errata to solve my issues with Guardian of Faith, but it went unaddressed and I'm wondering if maybe it's just not being brought up.

Guardian of Faith PHB
4th-level conjuration
Casting Time: 1 action
Range: 30 feet
Components: V
Duration: 8 hours
A Large spectral guardian appears and hovers for the duration in an unoccupied space of your choice that you can see within range. The guardian occupies that space and is indistinct except for a gleaming sword and shield emblazoned with the symbol of your deity. Any creature hostile to you that moves to a space within 10 feet of the guardian for the first time on a turn must succeed on a Dexterity saving throw. The creature takes 20 radiant damage on a failed save, or half as much damage on a successful one. The guardian vanishes when it has dealt a total of 60 damage.

I understand there's a lot of... controversy, maybe, around this spell. I've been in more than one heated discussion about the first sentence in the second paragraph. 

Any creature hostile to you that moves to a space within 10 feet of the guardian for the first time on a turn must succeed on a Dexterity saving throw.

The emboldened word in particular and a lack of a follow-up "or starts its turn there" brings a lot of misunderstanding to how this spell works in a literal translation and how people think it ought to work when read. I've read in other threads (particularly a direct ruling here) that creating effects on an area a creature already occupies does not necessitate they immediately proc the damage / save, so I understand spawning this Guardian and needing to wait for the creature's turn for the guardian's damage to be triggered. Beginning a turn does not equate to moving to the space that creature is already occupying. However, the literal reading of this spell implies that a creature hostile to the Guardian's caster could comfortably sit within the Guardian's reach for as long as it chose without triggering the Guardian's effect. Only by moving to any space within the Guardian's 10foot reach would trigger the Guardian's wrath. 

Secondly, I've also seen an argument that being pushed or pulled through the Guardian's area of effect would not trigger its attack because this wording implies a voluntary movement, despite the clarification that entering other areas of effect needn't be voluntary in the previous linked ruling. Given the stunning confusion of this Guardian's reactionary capability, that's hard to shut down. 

I'm not a fan of literal by-the-letter rulings but talk to / play with people who do so. Am I misunderstanding this already carefully-tailored spell, or am I right to think it leaves some clarification to be desired? 
Thanks

The 8 hour duration suggests that the spell is intended to guard during a long rest. If there are problems using it in combat, that might be because it wasn’t intended to be used in combat.

The phrasing of "moves to" is clear in that the damage is only triggered when the creature moves into such a space - this means that, yes, a creature can stay in a space and never trigger the guardian because it didn't move to a space. There is no ambiguity here. These are the definitions of the words. If you want to debate go debate the Oxford English Dictionary.

There is no distinction in the spell between voluntary or involuntary movement, just that the creature must move. Since the spell also states "first time on a turn" not "first time on its turn" means it is not referring to the movement specfically used for a turn. Spells and effects can let you "move"a creature. Move is move. If the spell was specifically referring to only voluntary movement then it would say so. It does not say so, so it doesn't. Move is just move - any kind is fine. So again, I see no real ambiguity here.

Only confusion is if teleportation would trigger the damage. Teleportation in D&D is not considered movement, which is why it is not given as a movement speed type, it does not provoke attacks of opportunity, doesn't trigger Booming Blade, etc. This is why they used "moves to" rather than "enters" and is the only game-specific distinction. However, teleport is not really specifically defined in such a way, despite being used as such in spells/etc. It leaves this open for debate.

If it says a turn, does that mean several different actors could use their turn in a single round to force several saves?

Moreover, if the guardian has dealt 50 damage, and a creature enters and fails it's save, does it take 10, or 20?  Is the 60 damage a hard cap or what happens?

Quote from mfloyd0232 >>

If it says a turn, does that mean several different actors could use their turn in a single round to force several saves?

 

Moreover, if the guardian has dealt 50 damage, and a creature enters and fails it's save, does it take 10, or 20?  Is the 60 damage a hard cap or what happens?

 
Frst question: yes. You can forcefully move a creature into one of the spaces once per turn over the course of the round. This is why the guardian's damage output is so low for the level and will disappear after a certain amount of damage has been dealt : to avoid overusing this mechanic.

Second question: the Guardian deals 20 damage per hit, with option to save after that. If the guardian had dealt 50 and a creature triggered the guardian, and failed the save it stll takes 20 and the guardian disappears.

Quote from Cyb3rM1nd >>

The phrasing of "moves to" is clear in that the damage is only triggered when the creature moves into such a space - this means that, yes, a creature can stay in a space and never trigger the guardian because it didn't move to a space. There is no ambiguity here. These are the definitions of the words. If you want to debate go debate the Oxford English Dictionary.

 

 I might not have communicated what I was talking about: I do recognize that the words are literally "move to." That's actually the entire point of that part of the post. You might notice how I referenced the errata and the hope that this wording, like so many other wordings, might be changed to no longer be this exact phrase! Again: the current wording is literally "moves to" and nothing else, and I have brought up this conversation not to debate what the current wording is, but what it should be. The idea that an entire round of combat, two rounds of combat, any indefinite number of rounds of combat could pass with a hostile creature sitting directly under the Guardian's watch without the Guardian fulfilling its very purpose is a little flabbergasting! There's also no mention of a sound produced, or a psychic alert to the caster when the Guardian strikes, or anything to suggest a player would know that the Guardian has encountered a hostile creature other than seeing it happen! Does that lack of wording suggest there is no light or sound or motion involved in the attack? 

Quote from Trirhabda >>

The 8 hour duration suggests that the spell is intended to guard during a long rest. If there are problems using it in combat, that might be because it wasn’t intended to be used in combat.

 I can understand that suggestion, except that to blindly follow that "suggestive" logic is to agree that a creature standing under the Guardian is suggested to provoke an attack as it sits beneath the Guardian on its turn, whose only purpose is to attack hostile creatures. And again, no mention of a sound produced, or a psychic alert to the caster when the Guardian strikes, or anything to suggest a player would know that the Guardian has encountered a hostile creature other than seeing it happen! Does that lack of wording suggest there is no light or sound or motion involved in the attack? Would any average creature be able to walk into the Guardian's range, take damage once, fire its spells or projectiles into the party as they sleep, and be completely unhindered the whole time it remained standing in the same spot? And that doesn't sound like some sort of oversight for a suggested long rest guardian spell? 
If it weren't meant to be used in combat, it wouldn't be based entirely around combat application. 

I don't think you understand the point of the spell. It's not a combat spell. The point is to put the guardian at an entrance like a door. If somebody entered the room to try and attack you in your sleep, wham, they get hit as would those following them in. Thus they are a little easier to take out. The range is 10' meaning anybody wanting to pass it is going to pass through at least 2 squares, potentially 3, if placed right taking damage each time. If this causes the creature to stop and stay there for the hours and hours to avoid the damage... Fantastic! Ambush avoided and the guardian did its job, hurrah! (how is that an oversight?) Do remember that of the 8 hour long rest, only 6 is actually spent sleeping - you're awake for the other 2. You will be awake before the spell runs out. You wake, see the enemy standing there and kill it, nice and easy. 

Also, it's not concentration and there is no limit to how many guardians you can place down beyond spell slots. If you have multiple spell slots of appropriate level.. use them all! You're about to complete a long rest to get them all back and if somebody does try to ambush you well they will get a lot of damage and you could take them out without anything more than cantrips or mace-bashing. Let's not forget you're in a party who may also have traps to set and there are nonmagical traps you can set up too.

Getting attacked and screaming out in pain and jumping around (dex save) will make noise and definitely breaks stealth.

Note also that you could use the Guardian's tendency to not attack a stationary target as a very effective guard over a prisoner. Tie the poor soul up 5' from the Guardian (or surrounded by many Guardians) and they dare not attempt an escape lest they be struck down. This is not an AoE damage spell, this is a spell designed to dissuade and punish any movement within an area. 

I would interpret the phrase “occupies that space” to mean hostile creatures cannot move through the space. That would make it very effective at choke points such as a doorway. The hostile creature would either have to take 60 points of damage to get by or it would need Dispel Magic.

The meaning of terms like “occupies that space” sometimes change slightly between different editions of the game so it might mean something else in 5th edition.

Does the phrase “hostile to you” mean that the creatures have to be actively attacking the caster? Interpreting this too narrowly could make the spell almost useless. The creature could move to within 10’ before attacking, attack and not trigger the spell. And if the creature doesn’t attack the caster specifically, can the spell “decide” that the creature is hostile to the caster as well?

Example: The party’s rogue has made some enemies. An assassin is sent to kill him. The assassin intends to kill the rogue without the rest of the party even knowing that the assassin is there so is he “hostile” to the party’s cleric, the caster of the spell. 

Too broadly and you can make this spell a “hostile thoughts” detector.

Example: The cleric of the temple casts Guardian of Faith at the entrance to the temple thus guaranteeing no one can enter who is “hostile” to the faith and by extension, hostile to the cleric who cast the spell.

Does the broad interpretation make the spell overpowered? It is a 4th level spell, how powerful should it be? 

Quote from Trirhabda >>

Does the phrase “hostile to you” mean that the creatures have to be actively attacking the caster? Interpreting this too narrowly could make the spell almost useless. The creature could move to within 10’ before attacking, attack and not trigger the spell. And if the creature doesn’t attack the caster specifically, can the spell “decide” that the creature is hostile to the caster as well?

Example: The party’s rogue has made some enemies. An assassin is sent to kill him. The assassin intends to kill the rogue without the rest of the party even knowing that the assassin is there so is he “hostile” to the party’s cleric, the caster of the spell. 

Too broadly and you can make this spell a “hostile thoughts” detector.

Example: The cleric of the temple casts Guardian of Faith at the entrance to the temple thus guaranteeing no one can enter who is “hostile” to the faith and by extension, hostile to the cleric who cast the spell.

Does the broad interpretation make the spell overpowered? It is a 4th level spell, how powerful should it be? 

This is another excellent series of questions. Those examples are hugely overpowered imo.  It's simplified by arbitration, like deciding that someone who is hostile to one player is hostile to all players, and that's fine, but that's still demanding the GM have some sort of answer to that even if they don't express it to the players. I really loathe sticking to the letter of the law as opposed to the spirit, but that's the issue I'm facing for the time being with more than just this spell. The rules are the rules, but they're written with the intent of being a guideline for DM's to follow. When questions arise and we default to the habit of looking for a precise definition it leaves this mess that doesn't feel satisfactory. I'll take your advice, Cybermind, and try to think of this as a different spell. 

Does the caster have to stay in the area? Or can the caster place a guardian somewhere and leave it as a trap?

Quote from Not_a_Crow >>

Does the caster have to stay in the area? Or can the caster place a guardian somewhere and leave it as a trap?

 If you have enough spell slots you could leave them behind you like a trail of breadcrumbs and they will still do their jobs for 8 hours, or until they hit their damage limit.

Quote from Not_a_Crow >>

Does the caster have to stay in the area? Or can the caster place a guardian somewhere and leave it as a trap?

 
You don't have to stay near it.

That could be fun for players and DMs alike!

Quote from Not_a_Crow >>

That could be fun for players and DMs alike!

 I thought so too.

Can the player MOVE the guardian, or is it permanently placed until it has used all its damage?

Quote from Vaders_Valkyrie >>

Can the player MOVE the guardian, or is it permanently placed until it has used all its damage?

 The guardian doesn't say it can be moved it it remains in the space it occupies.

To confirm, if a Hostile creature is within the 10-range prompting an attack, and the creature gets attack for the first turn it starts within the 10-foot range, does it get attacked again if it doesn't move in the 10-foot range? Or does it have to leave and reenter to prompt another attack?

Celestial Warlocks can cast quite a few of those as they always have two or three Spell Slots for them that they can get back with a Short Rest.