On Baptism by Tertullian
Chapter IX.--Types of the Red Sea, and the Water from the Rock.
How many, therefore, are the pleas of nature, how many the privileges of grace, how many the solemnities of discipline, the figures, the preparations, the prayers, which have ordained the sanctity of water? First, indeed, when the people, set unconditionally free, escaped the violence of the Egyptian king by crossing over through water, it was water that extinguished the king himself, with his entire forces. What figure more manifestly fulfilled in the sacrament of baptism? The nations are set free from the world by means of water, to wit: and the devil, their old tyrant, they leave quite behind, overwhelmed in the water. Again, water is restored from its defect of |bitterness| to its native grace of |sweetness| by the tree of Moses. That tree was Christ, restoring, to wit, of Himself, the veins of sometime envenomed and bitter nature into the all-salutary waters of baptism. This is the water which flowed continuously down for the people from the |accompanying rock;| for if Christ is |the Rock,| without doubt we see baptism blest by the water in Christ. How mighty is the grace of water, in the sight of God and His Christ, for the confirmation of baptism! Never is Christ without water: if, that is, He is Himself baptized in water; inaugurates in water the first rudimentary displays of His power, when invited to the nuptials; invites the thirsty, when He makes a discourse, to His own sempiternal water; approves, when teaching concerning love, among works of charity, the cup of water offered to a poor (child); recruits His strength at a well; walks over the water; willingly crosses the sea; ministers water to His disciples. Onward even to the passion does the witness of baptism last: while He is being surrendered to the cross, water intervenes; witness Pilate's hands: when He is wounded, forth from His side bursts water; witness the soldier's lance!