Petrichor

You gain a +1 bonus to attack and damage rolls made with this magic weapon. When you hit a fiend or an undead with it, that creature takes an extra 1d8 radiant damage.

While you hold the drawn sword, it creates an aura of bright light in a 10-foot radius around you and dim light out to a 20-foot radius. If you have 17 or more levels in the paladin class, the radius of the aura increases to 30 feet.

Sentience. Petrichor is intelligent and possesses INT 12 WIS 12, CHA 12 and is aligned to Lawful Good. The sword can communicate basic emotions to any creature carrying or wielding it and it can perceive its surroundings with normal hearing and vision out to 30ft. 

Personality. Petrichor is very sympathetic and caring. It keenly feels the suffering of living creatures and will insist it's wielder do something to alleviate the pains (emotional or physical) of those around it. 

The sword's primary purpose is to protect and serve the church of Ilmater, the Crying God. It will push it's wielder towards taking care of others and serving the interests of the faith. 

Once per day Ordeal may cast protection from evil and good on the wielder and it will maintain the concentration for the duration of the spell. 

Proficiency with a Longsword allows you to add your proficiency bonus to the attack roll for any attack you make with it.

Notes: Bonus: Magic, Damage: Radiant, Paladin, Damage, Combat, Versatile, Sap