John 17:3

Epistle of Ignatius to the Antiochians

The Evangelists, too, when they declared that the one Father was "the only true God,"[15]

Irenaeus Against Heresies Book IV

Now to whom is it not clear, that if the Lord had known many fathers and gods, He would not have taught His disciples to know [only] one God,[9]

Cyprian Epistle LXXII

But He, the same, sets forth, that it is the knowledge of the two which saves, when He says, "And this is life eternal, that they might know Thee, the only true God, and Jesus Christ, whom thou hast sent."[24]

Cyprian Treatise IV On the Lord's Prayer

Thus, when He taught what is life eternal, He embraced the sacrament of life in a large and divine brevity, saying, "And this is life eternal, that they might know Thee, the only and true God, and Jesus Christ, whom Thou hast sent."[76]

Cyprian Treatise V An Address to Demetrianus

Know God even late; for Christ at His coming admonishes and teaches this, saying, "This is life eternal, that they might know Thee, the only true God, and Jesus Christ, whom Thou hast sent."[43]

Cyprian Treatise XI Exhortation to Martyrdom Addressed to Fortunatus

And once more: "And this is life eternal, that they may know Thee, the only and true God, and Jesus Christ, whom Thou hast sent."[22]

Cyprian Treatise XII Three Books of Testimonies Against the Jews

And now, do Thou glorify me with Thyself, with the glory which I had with Thee before the world was made."[122]

A Treatise of Novatian Concerning the Trinity

If Christ was only man, wherefore did He lay down for us such a rule of believing as that in which He said, "And this is life eternal, that they should know Thee, the only and true God, and Jesus Christ, whom Thou hast sent? "[118]

Arnobius Against the Heathen Book II

jaws of death; that they can, nevertheless, have their lives prolonged by the favour and kindness of the Supreme Ruler if only they try and study to know Him,-for the knowledge of Him is a kind of vital leaven[220]

Lactantius Divine Institutes Book IV

And since these things are so, as we have shown, it is plain that no other hope of life is set before man, except that, laying aside vanities and wretched error, he should know God,[377]

Lactantius Divine Institutes Book VI

these except God, who has proposed to us virtue itself? Therefore the sum and substance of everything is contained in the acknowledging and worship of God; all the hope and safety of man centres in this; this is the first step of wisdom, to know who is our true Father, and to worship Him alone with the piety which is due to Him, to obey Him, to yield ourselves to His service with the utmost devotedness: let our entire acting, and care, and attention, be laid out in gaining His favour.[69]

Lactantius A Treatise on the Anger of God

But the second step is to perceive with the mind that there is but one Supreme God, whose power and providence made the world from the beginning, and afterwards continues to govern it. The third step is to know His Servant and Messenger,[4]

Constitutions of the Holy Apostles Book V

and by it have "known the one and only true God and Father,"[134]

Constitutions of the Holy Apostles Book VI

the same says in the Gospel, "That they might know Thee, the only true God."[136]

Origen Commentary on John Book II

To such persons we have to say that God on the one hand is Very God (Autotheos, God of Himself); and so the Saviour says in His prayer to the Father,[7]