I left out Mark’s baptism due to brevity.Like Philip Davis' discussion of the same event, I'm not sure I buy the whole cow, but again, there are some pertinent provocations in there. Looking forward to the book, although I hope there is some constructive work in there and not just the "not adoptionist" stuff.
First, I think Michael Peppard has shown that it is possible to read Mk 1.9-11 in an adoptionist sense, esp. if one regards eudokesa as meaning “chosen” and in light of Roman adoption practices. But I’m just not convinced that that is what Mark is trying to convey or how it was received by its initial readers.
Second, I don’t think Mark’s Gospel as a whole lends itself to adoptionism, since the demons somehow fear that Jesus is the Son who has “come” to destroy them (Mk 1.24; 5.7) and the Son belongs to a heavenly triad of Father, Son, and angels (Mk 13.32).
Third, if a divine voice calling Jesus “Son” marks out an adoption, then Jesus gets adopted three times at his baptism, transfiguration, and crucifixion. If one wanted to pick an adoption scene, Mk 15.39 would be preferable, as it would dovetail better with some notion of apotheosis.
Fourth, I don’t think Mk 1.11 tells us anything about when Jesus become the son, eudokesa could be gnomic. On a plain reading, I’d say that God is simply pleased that his Son has presented himself for baptism.
Fifth, the reception of the Spirit probably relates not to sonship but more to the prophetic nature of Jesus as the Isaianic servant given the allusion to Isa 42.1.
Let me know what you think :-)