The next heresy in B. Quash and M. Ward, Heresies and How to Avoid Them: Why It Matters What Christians Believe  concerns adoptionism: the view that believes in a double sonship for Christ. The chp is by Rachel Muers, a Quaker professor at Exeter.

First, he is Son of God by generation and nature; second, as a human he becomes God’s Son by adoption. This heresy was thought to separate the deity of Christ too sharply from his humanity. This view arose in the 8th Century, in Toledo Spain, and is connected to Elipandus. It was deemed heresy by Pope Hadrian I in 785 AD and at Frankfurt in 794.

Muers quickly reveals that the more popular view is that Jesus was adopted as God’s Son at the baptism. She knows the issue is more complex than this. Adoptionists, therefore, do not deny the Trinity and neither do they deny that the Son was/is eternally God. So, the issue is how to speak well of Jesus being the Son of God as a human.

Muer argues it is very important to affirm the humanity of Christ and not to make him less than human. Adoptionists wanted to affirm that everything God gives to Jesus, God gives to us. They pressed the doctrine of co-humanity to the extreme.

Her point as she sums up our collective faith: nothing could make Jesus God”s Son because he was — eternally — God’s Son. And this has to do with Jesus as example: he’s more than that. It’s his Sonship and his life, death, resurrection — and our participation in those events — that make us children of God, that give to us adoption.