We believe, teach, and confess that God's Son from eternity has been a particular, distinct, entire, divine person. Yet He is true, essential, perfect God with the Father and the Holy Sprit. In the fullness of time He received also the human nature into the unity of His person. He did not do this in such a way that there are now two persons or two Christs. Christ Jesus is now in one person at the same time true, eternal God, born of the Father from eternity, and a true man, born of the most blessed Virgin Mary. This is written in Romans 9:5, "from their race, according to the flesh, is the Christ who is God over all, blessed forever."
...since the incarnation, each nature in Christ does not exist by itself so that each is a separate person. These two natures are so united that they make up one single person, in which the divine and the received human nature are and exist at the same time. So now, since the incarnation, there belongs to the entire person of Christ personally not only His divine nature, but also His received human nature. So without His divinity, and also without His humanity, the person of Christ or the incarnate Son of God is not complete. We mean the Son of God who has received flesh and become man [John 1:14]. Christ is not two distinct persons, but one single person, even though two distinct natures are found in Him, unconfused in their natural essence and properties. (paragraphs 6, 11)
Condensed from CONCORDIA: THE LUTHERAN CONFESSIONS, copyright 2005,2006 by Concordia Publishing House. Used by permission. All rights reserved. To purchase a copy of CONCORDIA, call 800-325-3040.