All sin is an offense against God and a rejection of his perfect love and justice. Yet, Jesus makes a distinction between two types of sins. We call the most serious and grave sins, mortal sins. Mortal sins destroy the grace of God in the heart of the sinner. By their very grave nature, a mortal sin cuts our relationship off from God and turns man away from his creator.
This video explains everything that I wrote below. The video is NOT necessary to watch if you are going to read the following article. God Bless! -Catholica Romana
Why God became man? An answer from the Church Fathers, by Catholica Romana
Irenæus: Why Verbum caro factum est?
In Irenæus Against Heresies, Book V, Irenæus says that the Word had to become flesh, “for in no other way could we have learned the things of God, unless our Master, existing as the Word, had become man.” (The Writings of the Fathers 526) In order that we physically hear the Word, we must hear it from another human, and this makes logical sense. In order for our redemption, He gave His soul for our souls and His flesh for our flesh. God was incarnate so that we might be in communion with His immortality