The Baptism of Jesus, which we are commemorating today, fits into this logic of humility and solidarity: it is the action of the One who wanted to make himself one of us in everything and who truly joined the line of sinners; he, who knew no sin, let himself be treated as a sinner (cf. 2 Cor 5:21), to take upon his shoulders the burden of the sin of all humanity, including our own sin. He is the “servant” of Yahweh of whom the Prophet Isaiah spoke in the First Reading (cf. 42:1). His humility is dictated by the desire to establish full communion with humanity, by the desire to bring about true solidarity with man and with his human condition.
Jesus’ action anticipates the Cross, his acceptance of death for man’s sins. This act of abasement, by which Jesus wanted to comply totally with the loving plan of the Father and to conform himself with us, expresses the full harmony of will and intentions that exists between the Persons of the Most Holy Trinity. For this act of love, the Spirit of God revealed himself and descended to alight upon Jesus as a dove, and at that moment the love which unites Jesus to the Father was witnessed to all who were present at the Baptism by a voice from Heaven that everyone heard.
[Baptism] inserts [us] into this exchange of reciprocal love that is in God between the Father, the Son and the Holy Spirit…, God’s love is poured out upon [us], showering [us] with his gifts. …[C]leansed by the water, [we] are inserted into the very life of Jesus who died on the Cross to free us from sin and in rising, conquered death. Therefore, spiritually immersed in his death and Resurrection [we] are set free from original sin and the life of grace is born within [us], which is the very life of the Risen Jesus. He “gave himself for us”, St Paul says, “to redeem us from all iniquity and to purify for himself a people of his own who are zealous for good deeds” (Tit 2:14).
Benedict XVI, Homily for the Feast of the Baptism of the Lord, January 9, 2011