Baptism is the first of the sacraments of initiation, by which we mean the sacraments that get things going in the Christian life.
Our Lord himself directed that we are to baptise everybody in the name of the Father, and of the Son, and of the Holy Spirit, and from this we understand that it is very important to be baptised, as soon as we believe in the Lord (Mark 16:16; Matthew 28:19). Since the time of the apostles, the Church has baptised infants, too, as long as they are going to be brought up as Christians.
This is because Baptism does not just symbolise our changed relationship with God, it actually makes it happen. Original Sin, the responsibility all human beings inherit for the state of the world, for its alienation from God, is forgiven us, along with all sins we ourselves have committed. God’s sanctifying grace becomes available to us to help us in our growth towards him; we become God’s sons and daughters, since we become part of Christ’s body, the Church (1 Corinthians 12:12ff); the Holy Spirit takes up residence in our souls (Romans 8) – all this and much more. This is why the Church urges us to bring our babies for Baptism as soon as we can, so that the riches of God’s mercy and grace may be there for them from the very earliest days of their lives.