The importance of christology

In chapter 19 we see that christology is so important for Irenaeus because it is intrinsically linked to salvation.

"For it was for this end that 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 the adoption, might become the son of God."

If Jesus did not genuinely share in the divine life, or was not truly human, then salvation as Irenaeus understands it would be impossible.