When an undead fails its saving throw against your Turn Undead feature, the creature is instantly destroyed if its challenge rating is at or below a certain threshold, as shown in the Destroy Undead table:
DESTROY UNDEAD
Level Destroys Undead of CR
5th 1/2 or lower
8th 1 or lower
11th 2 or lower
14th 3 or lower
17th 4 or lower
1: DISCIPLE OF LIFE
Your healing spells are more effective. Whenever you use a spell of 1st level or higher to restore hit points to a creature, the creature regains additional hit points equal to 2 + the spell's level.
6: BLESSED HEALER
Beginning at 6th level, the healing spells you cast on others heal you as well. When you cast a spell of 1st level or higher that restores hit points to a creature other than you, you regain hit points equal to 2 + the spell's level.
8: DIVINE STRIKE
At 8th level, you gain the ability to infuse your weapon strikes with divine energy. Once on each of your turns when you hit a creature with a weapon attack, you can cause the attack to deal an extra 1d8 radiant damage to the target. When you reach 14th level, the extra damage increases to 2d8.
17: SUPREME HEALING
Starting at 17th level, when you would normally roll one or more dice to restore hit points with a spell,you instead use the highest number possible for each die. For example, instead of restoring 2d6 hit points to a creature, you restore 12.