http://www.ccel.org/ccel/mcgarvey/gospels.v.i.html
Jesus goes to be baptized by John. As he is coming up out of the water, the Spirit of God descends on him “like a dove”, meaning that the four writers of the Gospels do not want us to think that it was an actual dove. The voice of God affirms Jesus as His Son. The commentary points out that this reassurance may be important because the next thing that happens is that Jesus goes out into the wilderness and undergoes 40 days of prayer and meditation and temptation.