On the contrary, our Lord said (John 3:5): "Unless a man be born again of water and the Holy Ghost, he cannot enter into the kingdom of God."
I answer that, By Divine institution water is the proper matter of Baptism; and with reason. First, by reason of the very nature of Baptism, which is a regeneration unto spiritual life. And this answers to the nature of water in a special degree; wherefore seeds, from which all living things, viz. plants and animals are generated, are moist and akin to water. For this reason certain philosophers held that water is the first principle of all things.
Secondly, in regard to the effects of Baptism, to which the properties of water correspond. For by reason of its moistness it cleanses; and hence it fittingly signifies and causes the cleansing from sins. By reason of its coolness it tempers superfluous heat: wherefore it fittingly mitigates the concupiscence of the fomes. By reason of its transparency, it is susceptive of light; hence its adaptability to Baptism as the "sacrament of Faith."
Thirdly, because it is suitable for the signification of the mysteries of Christ, by which we are justified. For, as Chrysostom says (Hom. xxv in Joan.) on John 3:5, "Unless a man be born again," etc., "When we dip our heads under the water as in a kind of tomb our old man is buried, and being submerged is hidden below, and thence he rises again renewed."
Fourthly, because by being so universal and abundant, it is a matter suitable to our need of this sacrament: for it can easily be obtained everywhere.
Reply Obj. 1: Fire enlightens actively. But he who is baptized does not become an enlightener, but is enlightened by faith, which "cometh by hearing" (Rom. 10:17). Consequently water is more suitable, than fire, for Baptism.
But when we find it said: "He shall baptize you in the Holy Ghost and fire," we may understand fire, as Jerome says (In Matth. ii), to mean the Holy Ghost, Who appeared above the disciples under the form of fiery tongues (Acts 2:3). Or we may understand it to mean tribulation, as Chrysostom says (Hom. iii in Matth.): because tribulation washes away sin, and tempers concupiscence. Or again, as Hilary says (Super Matth. ii) that "when we have been baptized in the Holy Ghost," we still have to be "perfected by the fire of the judgment."
Reply Obj. 2: Wine and oil are not so commonly used for washing, as water. Neither do they wash so efficiently: for whatever is washed with them, contracts a certain smell therefrom; which is not the case if water be used. Moreover, they are not so universal or so abundant as water.
Reply Obj. 3: Water flowed from Christ's side to wash us; blood, to redeem us. Wherefore blood belongs to the sacrament of the Eucharist, while water belongs to the sacrament of Baptism. Yet this latter sacrament derives its cleansing virtue from the power of Christ's blood.
Reply Obj. 4: Christ's power flowed into all waters, by reason of, not connection of place, but likeness of species, as Augustine says in a sermon on the Epiphany (Append. Serm. cxxxv): "The blessing that flowed from the Saviour's Baptism, like a mystic river, swelled the course of every stream, and filled the channels of every spring."