One of the more tedious parts of performing a baptism is making sure that the paperwork is in order, and the names of the candidate and the godparents are correctly recorded in the register. Tedious though this is, it is a very important requirement, and not only because the candidate might need a baptism certificate in the future.
Those whose names are recorded in the register are witnesses to a marvellous sacrament; they are witnesses to Christ acting to cleanse the candidate from sin. They are witnesses to Christ's promise of eternal life; they are witnesses to salvation.
The idea that a baptism should be witnessed is not an innovation of the Church; we are only following the example the Scriptures record of the baptism of Christ. The evangelists, no doubt, are recording the testimony of human beings who were present at that event. However there is much greater testimony than this.
At the baptism of Christ, God himself, Father, Son and Spirit, gives testimony. Testimony not that Jesus is cleansed from his sins---for he has none---but testimony that Jesus Christ is the beloved Son of God upon whom the Father's favour rests.
The testimony given by writing a name in a baptismal register is rather tame compared to the testimony given when the heavens are torn apart, the Spirit descends like a dove and a voice booms from the sky.
But the baptism of Christ is not the final revelation of God in Jesus Christ. Neither Christ's birth, nor his baptism are the reason why he came. Jesus came, St John tells us in our second reading,
not with the water only,
by water and blood.
Jesus Christ came not only to be made man, and made manifest in his baptism, but to die on the Cross to save the human race. He came to reveal God's love for us, love that led Jesus Christ to die for us.
He opened the fountain of baptism that washes away our sins only by pouring out his blood, shown in the blood and water that flowed from his side after he was pierced by the soldier's lance. So both the water of his baptism and the blood of his crucifixion bear witness to the person and purpose of Jesus Christ.
St John adds to these witnesses a third, that of the Spirit. This is the same Spirit who is present in the form of a dove at the baptism, the same Spirit breathed forth by Jesus on the Cross, the same Spirit sent at Pentecost, and the same Spirit of truth that every Christian receives.
there are three witnesses, the Spirit, the water, and the blood; and these three agree.
Jesus is the Christ, the Son of God, the Word incarnate, who died to save us from sin.
These three witnesses remain with us in the Church today. In water we are baptised, we are cleansed from our sin by the power of Christ. We die with Christ and rise from the waters to new life with him in his Church.
With the blood of Christ, together with his body, in the sacrament of the Eucharist, we are present at the sacrifice that Jesus made of himself on the Cross, the sacrifice which atoned for our sins, and made effective the waters of baptism and all the other sacraments.
And the Spirit, though he is present in all we do, works in us especially through the sacrament of confirmation, where the Christian claimed for Christ in baptism is strengthen by the witness of the Spirit so that he himself can be a witness for Christ in an often hostile world.
So in these three sacraments of Christian initiation---Baptism, Confirmation and the Eucharist---we have received the divine witness to the person and mission of Jesus Christ, which we recall on this feast.
We receive and accept the testimony of human beings; how much more, then, should we receive and accept the testimony of God himself which is far greater, and ourselves be inspired to be witnesses to the marvellous things God has done for us.