Clerics (Casual)

Daru Spiritualist
Whenever a Cleric you control becomes the target of a spell or ability, it gets +0/+2 until end of turn.

Shaman en-Kor
0: The next 1 damage that would be dealt to Shaman en-Kor this turn is dealt to target creature you control instead.
1W: The next time a source would deal damage to target creature this turn, that damage is dealt to Shaman en-Kor instead.

Starlit Sanctum
Tap: Add 1 to your mana pool.
W, Tap, Sacrifice a Cleric: You gain life equal to that Cleric’s toughness.
B, Tap, Sacrifice a Cleric: Target player loses life equal to that Cleric’s power.

So the Combo works because there doesn't need to be a source of damage to use the Shaman en-Kor's ability. You are setting up a "redirection shield" similar in concept to a regeneration shield. Since the ability costs zero it can be done any number of times. Each time it is used and targets a Cleric, the Daru Spiritualist's ability will resolve and the result will be a cleric with a toughness equal to its original toughness+ 2* the number of times you have targeted with the Shaman en-Kor's ability. Then you just use the White activated ability of the Sanctum to gain that much life.

The combo can be done with anything that targets for zero mana (Lightning Greaves [needs to be two creatures on the board], Shuko) in place of the Shaman en-Kor.