AP: Not everything in the New Testament is explicit. But all the texts together are explicit, especially considering the context of the first century and comparison with other texts from the same period. Let me be direct: Mark, unlike Matthew and Luke, does not have an "infancy narrative.” But the story of Jesus’ baptism is clear:
Mark 1:10-11: “Immediately coming up out of the water, he saw the heavens opening, and the Spirit like a dove descending upon him; and a voice came out of the heavens: ‘You are my beloved Son, in you I am well-pleased.’”The scene is not historical. Mark, here, is quoting Psalm 2:7, an enthronement psalm of the king of Israel, who is but a mere man and is adopted as a special son of God at that time.
Acts 2:32-33, 36: “This Jesus God raised up again, to which we are all witnesses. Therefore having been exalted to the right hand of God, and having received from the Father the promise of the Holy Spirit, He has poured forth this which you both see and hear. . . . Therefore let all the house of Israel know for certain that God has made Him both Lord and Christ—this Jesus whom you crucified.”I think that by reading carefully and knowing the whole theology of the Son of God, which reaches its maximum clarity at the beginning of the Gospel of John, it's extremely clear.
TWH: Mark 1:10-11 is historical. Each of the Synoptics sought to include this account. So important is Jesus' baptism. Not only does it inaugurate the public ministry of Jesus, which begins after he returns from the wilderness having triumphantly resisted the devil, but it also gives us the first record of God speaking in the narrative. There are some issues surrounding the Synoptics that an interpreter has to deal with, such as whether the Father speaks directly to the Son ("You are my Son") or about the Son ("This is my Son"), or both (i.e., God the Father speaks twice at the baptism, once to the Son, once to others who can hear the proclamation). (I opt for the latter, by the way.) Sure, an interpreter has to wrestle with things like this, but wrestling with whether or not this actually happened? Are not the Gospels historical documents? I believe they are. And I believe they present the life of Jesus as it happened. And, so, Antonio and I disagree here.
Concerning the first point, the issue regarding the sonship of Jesus Christ is no stranger to evangelicalism. Should we affirm the "eternal sonship" view or the "incarnational sonship" view? The former says Jesus has always been God's Son, even before his incarnation, baptism, crucifixion, and resurrection. Jesus is God's Son today, just as he was God's Son before the foundation of the world. The latter says that Jesus became God's Son at his resurrection, a position which understands "Son" as a title, not a description of Jesus' essence. The declaration at Jesus' baptism, however, is but one of the many supports for the "eternal sonship" view. God the Father says Jesus is his beloved Son, the stative verb in the passage indicating there an unchanging characteristic of who Jesus is.
One of the most well known evangelical Bible teachers in America (though he is also known throughout the Spanish-speaking world via the Spanish version of his radio ministry, Gracia a Vosotros) used to ascribe to the "incarnational" view. If you are curious on reading why he changed his position, you can find his answer here.