So too our own baptisms make us sons and daughters of God; and we become members of the broader community of the Church. Baptism announces publicly our new relationship to God as it washes away our sin and pours out Grace into our hearts.
But why did Jesus undergo this ritual? He was already God’s Son, and so no re-birth was necessary. He was without sin, and so the cleansing of sin was not needed. And certainly Jesus did not require Grace – he is the very fount of Grace.
John the Baptist must have realized all of this when He said to Jesus: “I need to be baptized by you, and do you come to me?” (Matthew 3:14) But Jesus replied: “Let it be so now; it is proper for us to do this to fulfill all righteousness.” (15)
Why was this the “proper” thing to do?
For an answer we turn to St. Thomas Aquinas, who, in his Summa Theologica (Question 39, Article 1) takes up the challenge as to whether it was fitting that Christ be baptized…
“It was fitting for Christ to be baptized. First, because, as Ambrose says on Luke 3:21: ‘Our Lord was baptized because He wished, not to be cleansed, but to cleanse the waters, that, being purified by the flesh of Christ that knew no sin, they might have the virtue of baptism’; and, as Chrysostom says (Hom. iv in Matth.), ‘that He might bequeath the sanctified waters to those who were to be baptized afterwards.’ Secondly, as Chrysostom says (Hom. iv in Matth.), ‘although Christ was not a sinner, yet did He take a sinful nature and 'the likeness of sinful flesh.' Wherefore, though He needed not baptism for His own sake, yet carnal nature in others had need thereof.’ And, as Gregory Nazianzen says (Orat. xxxix) ‘Christ was baptized that He might plunge the old Adam entirely in the water.’…”
It is helpful to recall here the Church’s ceremony at the Easter Vigil, when the baptismal waters are blessed with the Paschal Candle. The Paschal Candle (the large candle marked with a cross and used throughout the year to represent Christ, the Light of the World) is dipped into the baptismal fount and three times (in the name of the Father, and of the Son, and of the Holy Spirit) and thus the waters are broken and made fertile to baptism new Christians. In a sense the waters must be baptized by Christ before we can be baptized by the waters.
Jesus plunges into the waters of baptism not for His own sake, but for ours. As He tells John, “it is proper for us to do this to fulfill all righteousness.” Our own righteousness is fulfilled by Christ’s presence in the baptismal waters. He has passed through those waters before us and His presence there makes the Sacrament effective for our salvation.