The clerics pray to the gods like they always have, but you look at the changes the gods want made and get them done instead of sitting around praying like the other followers do. You root out corruption within your own temples and society, and put it down with a divine purpose behind that dagger. 

As a Mystic, you have seen how little it pays off to sit around on your ass and do nothing to better the world. To progress the will of your god, you must act, and what better way to start acting than to listen to the hints left by the divine and picking up on them. Mystics are holy assassins, infiltrators and people who do what must be done to get shitty tyrants away from the lands that the gods servants work so hard for.

Study of Divinity

At 3rd level, You gain proficiency in Religion and History from your history and knowledge of whatever deity you devote yourself too. You also double your proficiency bonus for any rolls you make with any such rolls (expertise)

God's Will

Starting at 3rd level, your divine purpose fuels your attacks. Whenever you deal damage with your Sneak Attack feature, you may choose to turn all damage from this attack to radiant or necrotic based on the nature of your chosen deity and you deal additional damage equal to your Rogue level.

 

When you deal damage in this way, the creature becomes marked with holy energy. This mark lasts 10 minutes or until you lose concentration, and while marked, the creature glows with a radiant energy of which only you can see. You can see this aura through 1 foot of stone, 1 inch of common metal, or up to 3 feet of wood or dirt. Thicker substances block the vision, as does a thin sheet of lead. 

 

You can use the feature an amount of times equal to your proficiency bonus per long rest.

Necrotic

The damage from The Gods Will is Necrotic

Radiant

The damage from The Gods Will is Radiant

Signs of the Gods

At 9th level, you gain the ability to look for the signs of your deity when you need to know what move to make. You gain the ability to look for the signs of your deity whenever you’re in need. You may cast Commune as an Action once per short rest.

Purge the Unworthy

At 13th level, your divine fury pushes you to complete the tasks at hand. While you have a hostile target marked by your God’s Will feature, you gain the following benefits: 

• Your movement increases by 10 feet. 
• Once per turn when you take the Attack action to make against your Marked target, you can make an additional attack against it.
• You may use your bonus action to give yourself advantage on attack rolls against the marked creature until the end of your current turn.

Divine Determination

At 17th level, your deity’s powers restore your energy whenever you complete the task at hand. When you kill a creature that has been marked by your God’s Will feature and is of CR 2 or higher, you regain hit points equal to 5 + your Rogue-level and one use of your God’s Will feature.