From the book On the Holy Spirit by Saint Basil the Great, bishop (4th century)
Our Lord made a covenant with us through baptism in order to give us eternal life. There is in baptism an image both of death and of life, the water being the symbol of death, the Spirit giving the pledge of life. The association of water and the Spirit is explained by the twofold purpose for which baptism was instituted, namely, to destroy the sin in us so that it could never again give birth to death, and to enable us to live by the Spirit and so win the reward of holiness.
The water into which the body enters as into a tomb symbolizes death; the Spirit instills into us his life-giving power, awakening our souls from the death of sin to the life that they had in the beginning. This then is what it means to be born again of water and the Spirit: we die in the water, and we come to life again through the Spirit.
To signify this death and to enlighten the baptized by transmitting to them knowledge of God, the great sacrament of baptism is administered by means of a triple immersion and the invocation of each of the three divine Persons. Whatever grace there is in the water comes not from its own nature but from the presence of the Spirit, since baptism is not a cleansing of the body, but a pledge made to God from a clear conscience. […]
As a preparation for our life after the resurrection, our Lord tells us in the gospel how we should live… Through the Holy Spirit we are restored to paradise, we ascend to the kingdom of heaven, and… blessing is showered upon us, both in this world and in the world to come.
Apse mosaic, 9th century. Basilica di Santa Cecilia in Trastevere, Rome.