Luke’s picture of Christ in the water with “all the people” (vs 21) shows us that what happens to Jesus at his baptism happens to us, to be baptised is to share Christ’s life. We can understand this in terms of the Trinity.
In the first instance baptism unites us to the Son. John points to Jesus’ as the true bridegroom, and Christians are his bride; we are united to him, just as a husband and wife are “one”. The water of baptism is like the Mikvah bath that cleansed Jewish brides before their wedding. This understanding of being united with Christ is important for our faith, because it helps us see the other graces that come to us in salvation, we share in everything that Jesus has. Union also helps us understand the Christian life: Christ’s love for us is like the perfect husband who cares for his wife like his own body; when we pray, we are praying with the Son to the Father; when we worship, we worship the Father with the Son; we avoid sin because we belong to him; and we can love others because we share his power; we are changed until we conform to him perfectly.
Secondly, because we are united to Christ, we share in his sonship and become children of God by adoption. The words of the Father to the Son, “You are my Son, the Beloved; with you I am well pleased” now apply to us too. The waters of baptism are like the waters of birth, they begin this new life as a child of God. The Father is pleased because he sees us clothed in the righteousness of Christ. But that is not God tricking himself into accepting us. Rather, it is his delight in who we will be when we are perfectly like Jesus and fully ourselves, glorifying him uniquely. Even more wonderfully, he delights in us even now, in our sin and weakness, like a parent who loves their young child. Even our imperfection reveals in some way what we will one day be in Christ, and enables us to understand God’s love for us. Understanding this helps us to feel accepted by God and to accept one another.
Thirdly, baptism causes us to be baptised in the Holy Spirit. Just as the Spirit descends and rests on Jesus, so the Spirit descends and rests on us, because we are united to him. Pointing to Noah, the dove represents the shalom of God that followed the judgement of the flood, the peace that led to new life and fruitfulness. The Holy Spirit transforms our way of experiencing the world so that it is like Christ’s. In place of the fear that characterises the children of Adam comes the perfect peace that enabled Jesus to live in the knowledge of his Father’s love in all things, even at his crucifixion. From this peace flow all of the gifts and fruit of the Spirit, and ultimately the fullness of eternal life, when we shall see God’s glory in all things, as the waters cover the sea.