O Sweet Exchange!

The Letter to Diognetus was written in the second century around 125 A.D. We don't know who wrote it but it it the oldest existing statement on the work of substitution that Christ underwent for us. Read, reflect, and meditate on it. It is a beautiful statement.
Letter to Diognetus
O, the surpassing kindness and love of God! He did not hate us, or reject us, or bear a grudge against us. Instead, he was patient and forbearing; in his mercy he took upon himself our sins. He himself gave up his own Son as a ransom for us—the holy one for the lawless, the guiltless for the guilty, “the just for the unjust” (1 Pet 3:18), the incorruptible for the corruptible, the immortal for the mortal. For what else but his righteousness could have covered our sins? In whom was it possible for us, the lawless and ungodly, to be justified, except in the Son of God alone? O the sweet exchange! O the incomprehensible work of God! O the unexpected blessings, that the sinfulness of many should be hidden in one righteous man, while the righteousness of one should justify many sinners!