St. Justin Martyr (100–165) was a second-century Christian apologist and one of our earliest testimonies to the worship of the Early Church. A pagan convert, he died a Christian martyr in Rome. In St. Justin’s First Apology (ca. 150), he writes regarding Christian Baptism:
I will also relate the manner in which we dedicated ourselves to God when we had been made new through Christ; lest, if we omit this, we seem to be unfair in the explanation we are making. As many as are persuaded and believe that what we teach and say is true, and undertake to be able to live accordingly, are instructed to pray and to entreat God with fasting, for the remission of their sins that are past, we praying and fasting with them. Then they are brought by us where there is water, and are regenerated in the same manner in which we were ourselves regenerated. For, in the name of God, the Father and Lord of the universe, and of our Saviour Jesus Christ, and of the Holy Spirit, they then receive the washing with water. For Christ also said, “Unless you be born again, you shall not enter into the kingdom of heaven” (John 3:5). Now, that it is impossible for those who have once been born to enter into their mothers’ wombs, is manifest to all. And how those who have sinned and repent shall escape their sins, is declared by Esaias [Isaiah] the prophet, as I wrote above; he thus speaks: “Wash you, make you clean; put away the evil of your doings from your souls; learn to do well; judge the fatherless, and plead for the widow: and come and let us reason together, says the Lord. And though your sins be as scarlet, I will make them white like wool; and though they be as crimson, I will make them white as snow. But if you refuse and rebel, the sword shall devour you: for the mouth of the Lord has spoken it” (Isaiah 1:16-20).
And for this [rite] we have learned from the apostles this reason. Since at our birth we were born without our own knowledge or choice, by our parents coming together, and were brought up in bad habits and wicked training; in order that we may not remain the children of necessity and of ignorance, but may become the children of choice and knowledge, and may obtain in the water the remission of sins formerly committed, there is pronounced over him who chooses to be born again, and has repented of his sins, the name of God the Father and Lord of the universe; he who leads to the laver the person that is to be washed calling him by this name alone. For no one can utter the name of the ineffable God; and if any one dare to say that there is a name, he raves with a hopeless madness. And this washing is called illumination, because they who learn these things are illuminated in their understandings. And in the name of Jesus Christ, who was crucified under Pontius Pilate, and in the name of the Holy Ghost, who through the prophets foretold all things about Jesus, he who is illuminated is washed.
—St. Justin Martyr
First Apology 61