O Sweet Exchange!
I love this. From the anonymous writer "Mathetes" (which means "disciple") to Diognetus, dated to the late 2nd century, I believe. I highlighted my favorite part in blue :)
9:1 Having thus planned everything already in Hismind with His Son, He permitted us during the former time to be borne along by disorderly impulses as we desired, led astray by pleasures and lusts, not at all because He took delight in our sins, but because He bore with us, not because He approved of the past season of iniquity, but because He was creating the present season of righteousness, that, being convicted in the past time by our own deeds as unworthy of life, we might now be made deserving by the goodness of God, and having made clear our inability to enter into the kingdom of God of ourselves, might be enabled by the ability of God.
9:2 And when our iniquity had been fully accomplished, and it had been made perfectly manifest that punishment and death were expected as its recompense, and the season came which God had ordained, when henceforth He should manifest His goodness and power (O the exceeding great kindness and love of God), He hated us not, neither rejected us, nor bore us malice, but was long-suffering and patient, and in pity for us took upon Himself our sins, and Himself parted with His own Son as a ransom for us, the holy for the lawless, the guileless for the evil, _the just for the unjust,_ the incorruptible for the corruptible, the immortal for the mortal.
9:3 For what else but His righteousness would have covered our sins?
9:4 In whom was it possible for us lawless and ungodly men to have been justified, save only in the Son of God?
9:5 O the sweet exchange, O the inscrutable creation, O the unexpected benefits; that the iniquity of many should be concealed in One Righteous Man, and the righteousness of One should justify many that are iniquitous!
9:6 Having then in the former time demonstrated the inability of our nature to obtain life, and having now revealed a Saviour able to save even creatures which have no ability, He willed that for both reasons we should believe in His goodness and should regard Him as nurse, father, teacher, counsellor, physician,mind, light, honour, glory, strength and life.
here is the entire epistle:
for a different translation, look here: