This refers to God, in the person of Jesus, taking on human nature – becoming Emmanuel, ‘God with us’. As completely both God and man, He laid aside His divinity and took on the limitations of humanity so He could show us how to live a life pleasing to God and to provide salvation for all who believe in Him (Phil 2:6-11). Jesus was born, becoming ‘flesh’ and lived among us (Mt 1:20-23; Jn 1:1-14; Rom 1:2-5; 1 Jn 1:1-3, 4:1). His birth, celebrated at Christmas was the advent (arrival) of God incarnate.
Jesus became a human to restore to us what was forfeited through Adam
righteousness (Jn 5:30; 2 Cor 5:21; Gal 4:4,5; Heb 2:18, 5:8). His blood cleanses from all sin and brings us into a right relationship with God (Eph 2:13; Heb 10:19; 1 Jn 1:7).
Through His incarnation He identified with us, experiencing the trials and tests common to humanity, and so is able to sympathize with us and aid us (Heb 4:15). Those who confess Jesus has ‘come in the flesh’ are of God, but this belief must be personally activated for such a person to be a true Christian. However if a person does not confess that Jesus came in the flesh they are neither a Christian nor to be recognised as a Christian teacher, but are against God (1 Jn 4:2,3). If Jesus was not a man, then all that occurred in His life and on the cross was in ‘appearance’ only, and was a delusion. This would mean no blood shed and thus no salvation or resurrection (1 Cor 15:1-22). However, praise God, He did come and die in our place and rise again, victorious. This is the glorious hope of the Christian faith.
Incarnation is not to be confused with reincarnation, which is the belief of some Eastern religions that the soul is reborn in a new and different body after death in a previous life.
See also: human/humanity, reincarnation.