γνῶθι σεαυτόν, know yourself (source)
The saying “Know yourself” means therefore that we should recognize and acknowledge in ourselves the God who made us in his own image, for if we do this, we in turn will be recognized and acknowledged by our Maker. So let us not be at enmity with ourselves, but change our way of life without delay. “For Christ who is God, exalted above all creation,” has taken away our sin and has refashioned our fallen nature. In the beginning God made us in his image and so gave proof of his love for us. If we obey his holy commandments and learn to imitate his goodness, we shall be like him and he will honor us. God is not beggarly, and for the sake of his own glory he has given us a share in his divinity.
- Hippolytus (c. 236), On the Refutation of all Heresies 10, 33-34: PG 16, 3452-3453, found in J. Robert Wright, Readings for the Daily Office from the Early Church, 37.