Not every agent of a Church can be a mighty Paladin or a lofty Cleric, or even a simple Priest. Some servants of gods employ a different skillset entirely, for different roles. Whoever the enemies of their Church may be: witches, heretics, or simply those who would do the Church harm, some Rogues combine their skills with magic gifted them by their god to root out and eliminate those enemies.

Spellcasting

When you reach 3rd level, you gain the ability to cast spells. See chapter 10 for the general rules of spellcasting and chapter 11 for the Cleric spell list.

Cantrips. You learn two cantrips from the Cleric spell list. You learn another Cleric cantrip of your choice at 10th level.

Spell Slots. Make use of the Arcane Trickster spellcasting table (p. 98, PHB) to tell you how many spell slots you have to cast your spells of 1st level and higher. To cast one of these spells, you must expend a slot of the spell's level or higher. You regain all expended spell slots when you finish a long rest.

For example, if you know the 1st level spell detect magic and have a 1st-level and a 2nd-level spell slot available, you can cast detect magic using either slot.

Spells Known of 1st-Level and Higher. You know three 1st level Cleric spells of your choice, two of which you must choose from the divination, enchantment, or necromancy spells on the Cleric spell list.

The Spells Known column of the Arcane Trickster Spellcasting Table shows when you can learn more Cleric spells of 1st-level or higher. Each of these spells must be a divination, enchantment or necromancy spell of your choice, and must be of a level for which you have spell slots. For instance, when you reach 7th level in this class, you can learn one new spell of 1st or 2nd level.

The spells you learn at 8th, 14th and 20th level can come from any school of magic.

Whenever you gain a level in this class, you can replace one of the Cleric spells you know with another spell of your choice from the Cleric spell list. The new spell must be of a level for which you have spell slots, and it must be a divination, enchantment or necromancy spell, unless you're replacing the spell you gained at 8th, 14th or 20th level.

Spellcasting Ability. Wisdom is your spellcasting ability for your Cleric spells, since your magic draws from your connection to your god. You use your Wisdom whenever a spell refers to your spellcasting ability. In addition, you use your Wisdom modifier when setting the saving throw DC for a Cleric spell you cast and when making an attack roll with one.

Spell Save DC = 8 + your proficiency bonus + your Wisdom modifier.