The term is important in Christology, in the sense that most Christian denominations teach that the Son of God did not undergo any change in his divine nature at the Incarnation. Immutability implies in this particular understanding that the Holy Trinity cannot change and remains united. In Christian theology the idea of God's immutability is essentially tied to God's eternality. God, being out side of time (trans-temporal), can not change, because he is not affected by time, which is the agent of change in a temporal universe.