MARK 1:9-11: 9 At that time Jesus came from Nazareth in Galilee and was baptized by John in the Jordan. 10 Just as Jesus was coming up out of the water, he saw heaven being torn open and the Spirit descending on him like a dove. 11 And a voice came from heaven: "You are my Son, whom I love; with you I am well pleased."
John Calvin: A loud verse was heard that his majesty might be more impressive. The public appearance of Christ, to begin the office of Mediator was accompanied by this announcement, so that we too may know we are adopted and boldly call God Father. The title of "Son" belongs truly and naturally to Christ alone, but he was declared to be the Son of God in human flesh, so that we may also obtain this blessing of calling God Father. So when God presents Christ as Mediator accompanied by the title "Son" he indicates that He is the Father of us all (Eph. 4:6)
Thoughts: On this Trinity Sunday, this verse is a great meditation. For the three persons of the godhead were all present at once- the Father's voice, the Son in the water, and the Spirit descending like a dove. The voice from heaven indicates the great love the Father has for the Son. The Trinity is a threefold power of love mixed with truth. I love my son. But there are times when I do things to alienate my son, and my son does things to alienate himself from me. But Jesus does nothing to alienate himself from God- He is sinless. The Father does nothing to alienate himself form the Son. Jonathan Edwards spoke of the Holy Spirit as the eternal love that flows between the Father and the Son. In a world that often does not believe in true love- God shows us in his very essence that He is love. In a world that has a tendency toward alienation, isolation, separation- God shows us reconciliation, unity, and true love. There have been human trinities- but they all fail. There was the first Roman triumvirate with Julius Caesar and Pompeii (and Crassus who died) in which they ended up in war. There was the second triumvirate that ended up in civil war between Mark Antony and Augustus Caesar. Or in more modern history there was Churchill, FDR, and Stalin- that ended up in the cold war that could have destroyed the whole earth. But God's trinity is the trinity of love- and sets the ultimate example of love for us.