In the Communion Gospel this Sunday from the 1928 Book of Common Prayer, we have this in part:
And they asked him, and said unto him, Why baptizest thou then, if thou be not that Christ, nor Elias, neither that prophet? John answered them, saying, I baptize with water: but there standeth one among you, whom ye know not; He it is, who coming after me is preferred before me, whose shoe’s latchet I am not worthy to unloose.(John 1:25-27 KJV)
Bossuet explains this in his The Preaching of Saint John the Baptist. 5, The baptism of John and that of Jesus Christ, from the Elevations on the Mysteries:
When Saint John opposes the water of his baptism to the fire of that of Jesus Christ, and when Jesus Christ himself explained that this baptism of fire and of the Holy Spirit is the one with which the disciples were flooded on the day of Pentecost, we understand that we must not believe that the baptism of Jesus Christ is not like that of John’s baptism, but it is that John’s contained only simple water, instead of the water that Jesus gave was full of the Holy Spirit and a celestial fire, that is to say of the same fire of the Holy Spirit whose flood poured out on the whole Church in the upper room. It is this fire which still animates the water of baptism today, and which makes the Saviour say: That we have no part in his kingdom unless we are reborn from the water and the Holy Spirit, that is to say, in the mystical language, if one is not reborn from water and fire.
Here then is the consolation. The water of the baptism of Jesus Christ is not empty and sterile water; the Holy Spirit animates it and makes it fruitful; by washing the body it inflames the heart; if you do not come out of the baptism full of the heavenly fire of the love of God, it is not the baptism of Jesus Christ that you have received. Christian penance, which is nothing more than a second baptism, must be animated with the same fire: He to whom more is given must also, says the Saviour, love more. When you have only the tears that terror causes to shed, it is still only the water and the baptism of John. When you begin to love God as the author and source of all righteousness, Jesus begins to baptize you internally with his fire, and his sacrament will complete the work.