Pre-existence of Christ

The pre-existence of Christ is the belief that Jesus did exist before he was even born. Before his human birth he was the fully divine person God the Son until he chose to be "made flesh" to then possess not one—but two natures—human and divine.
In John 17:5, Jesus talks about the glory that he had with the Father "before the world existed" and in verse 24, that the Father loved him "before the foundation of the world". 
John 1 opens with "In the beginning was the Word, and the Word was with God..." this "Word" is later said to have been Jesus in verse 14 but just "made flesh".
Nicene Christianity.
The pre-existence of Christ is one of the most important beliefs in mainstream Christianity. Most mainstream churches that accept the Nicene Creed view the nature of the pre-existent Christ as the fully divine person called the Word, which is described in John 1:1-3; the verses read: