What was Jesus writing in the sand in John 8? It’s quite obvious for Ambrose of Milan. The context is a letter written to Studius (a layman apparently and a judge) against capital punishment:
“Here is the reply our Saviour gives to all such questions. When the Jews caught the adulteress, they brought her under guard to the Savior, to see if he would let her go, and so abolish the law of which he said “I have not come to abolish the law, but to fulfill it” (Matt. 5:17), or if he would condemn her and so run up against a limit to his purpose of redemption. Anticipating it all, the Lord Jesus stooped down and “wrote upon the ground.” As for what he wrote, the text from the prophet Jeremiah about King Jeconiah tells us: “Earth, earth…write these men down as forsaken!” (Jer. 22:29f.). The names of the Jewish accusers are written on the ground; the names of believing Christians are written in heaven. On the ground are the names of those forsaken by their true father, who have tempted him and brought reproach against the author of salvation. Faced with Jewish accusers, Jesus lowers his head, and then, since he “has nowhere to lay his head,” raises it again as though to pronounce judgement, saying ” ‘Let him who is without sin be the first to throw a stone!’ Again he lowered his head and wrote on the ground. Hearing this, they began to leave, one by one, beginning with the eldest” (John 8:7-9). Perhaps they had more on their consciences, having lived longer; or perhaps they had acquired more discretion and saw the force of his judgement more quickly. Anyway, having first come to accuse someone else’s fault, now they began to experience compunction at their own.”
Now you know.
Excerpted from “Letter 50,” translated by eds. from Corpus Scriptorum Ecclesiasicorum Latinorum, vol. 82 as found in Oliver O’Donovan and Jane Lockwood O’Donovan, eds. From Irenaeus to Grotius: A Sourcebook in Christian Political Thought (Grand Rapids: Eerdmans, 1999).