Cleric Class

An ability that triggers “whenever you gain life” triggers just once for each life gain event, no matter how much life you gain.

Each creature with lifelink dealing combat damage causes a separate life gain event. For example, if two creatures you control with lifelink deal combat damage at the same time, you will gain 2 additional life from Cleric Class's first ability and its level 2 ability will trigger twice. However, if a single creature you control with lifelink deals combat damage to multiple creatures, players, and/or planeswalkers at the same time (perhaps because it has trample or was blocked by more than one creature), you will only gain 1 additional life and the ability will trigger only once.

If you gain an amount of life “for each” of something, that life is gained as one event and the ability will trigger only once.

You can't activate the first level ability of a Class unless that Class is level 1. Similarly, you can't activate the second level ability of a Class unless that Class is level 2.

Gaining a level won't remove abilities that a Class had at a previous level.

Each Class starts with only the first of three class abilities. As the first level ability resolves, the Class becomes level 2 and gains the second class ability. As the second level ability resolves, the Class becomes level 3 and gains the third class ability.