"The Word of God was made man, and he who was the Son of God
became the Son of Man, that man, having been taken into the Word,
and receiving adoption, might become the son of God. For by no other means
could we have attained to incorruptibility and immortality,
unless we had been united to incorruptibility and immortality"
Irenaeus of Lyons writing on the Christians' participation in God
This quote is kind of a mouthful. It doesn't help that it was written around the year 180 A.D. But, Irenaeus so beautifully captures such a central tenant to the gospel. The wonderful news of the gospel is this (and this is slight translation of what Irenaeus wrote above):
The 2nd person of the trinity, who had existed from all eternity, became man. The Son of God became the Son of Man. This is who Jesus Christ is. He did this, so that man (us), might be united to the Son of God (Jesus Christ), so that we could receive the same sonship that he has. We can be adopted as sons of God because we are directly united to the Son of God. We can only be restored to spotless perfection and eternal life by being united to the very one who himself is spotless, perfect, and from eternity.
The Christian life is not a bunch of rules to follow or information to believe. It is living in this union with Christ. It is sharing in this life.