Cyril of Jerusalem

For since a person's nature is twofold, compounded of soul and body, the purification is also twofold, incorporeal for the incorporeal part, bodily for the body. For as the water purifies the body, so the Spirit seals the soul, that having our hearts sprinkled and our bodies washed with clean water, we may draw near to God. Therefore, when about to enter the water, do not regard it as mere water, but look for its saving power by the efficacy of the Holy Spirit, for without both you cannot be made perfect. It is not I who say this, but the Lord Jesus, who has the power in this matter, says, "Unless one is born of water and the Spirit, he cannot enter the kingdom of God." Neither does he who is baptized but has not been deemed worthy of the Spirit possess perfect grace; nor will one who acts virtuously, but does not receive the seal by water, enter into the kingdom of heaven. This may appear a bold saying, but it is not mine, for it was Jesus who pronounced it.