Any spell tooltip with orange numbers in-game is scaled from your Power.
The base power for all classes is 813
If a spell says it does 1238 damage in orange The ratio would be 1283/813 = 1.522. So any time you cast that spell the real damage deal is 1.522 * curent power
There are multiplicative and additive power boosts :
Ex: Gospel of Onslaught gives a multiplicative power boost
Ex: Enrage Increases Power by 144