The Baptism of Jesus is initially perplexing to us, as we know that John has called out for baptism for the sake "of remission of sins". Knowing Jesus to be sinless, the act can seem awkward in the Gospel. John himself notes this when he baptized Jesus and says to him "it is you who should be baptizing me!" and Jesus replies, "let it be, to fulfill all righteousness".
So Jesus is baptized to fulfill all righteousness. What does this possibly mean?
Of course in Judaism, righteousness means obedience to the Torah. By fulfillfing righteousness, Jesus is indicating his complete oneness with the will of the Father.
Benedict XVI writes that
"on the one hand, immersion into the waters is a symbol of death, which recalls the death symbolism of the annhilating, destructive power of the ocean flood. The ancient mind percieved the ocean as a permanent threat to the cosmos and the earth. It was the primeveal flood that might submerge all life."
This can be seen, of course, in Genesis where the Spirit of God subdues the powers of the great deep, and the fear of the ocean is accented in the account of the Flood. The great cosmic enemy in Jewish mythology was always the "water serpent" , which God destroys in the Pslams. This also sheds significance on Jesus' acts of walking on water because in doing so he subdues it.
Yet the flowing waters of the river are, above all, the symbol of life.
So we can see that there is a death/life theme inherent in the act of baptism, the sumbergence into the waters and the rising up again.
Pope Benedict writes that the significance of this event [Baptism] could not fully be comprehended until it was done so in the light of the Crucifixion and the Resurrection.
Now if we consider that the baptism of John was for the remission of sins and take note of Christ's atoning death, the baptism falls into place. The baptism of Jesus was the inaugurating event of his public ministry, and Benedict writes that
"He inaugurated his public activity by stepping into the place of sinners. His inaugural gesture is an anticipation of the Cross. He is, as it were, the true Jonah who said to the crew of the ship, "Take me and throw me into the sea". The Baptism is an acceptance of death for the sins of humanity
The imagery that we arrive to in the gospel is one of the sinless Son of God, stepping into the place of sinners in the waters, stepping before us and leading us, acting as a sign to us, in the way of repentence.
Submerged under water, we are all familiar with that moment our head goes under and the sounds of the world around us, the sounds of life, are cut off. Our eyes go closed, the light dims and, with the water all around us, we can not help but feel alone. That is until we swim to the top again, break the surface and the busy sounds and sights of life are there just as we left them.
Thus baptism becomes a profound anticipation of the Crucifixion and Resurrection.