Q: In the scene in which Jesus saves the woman caught in adultery from being stoned, we see Him writing in the sand. What is the significance of this act?
The scene is taken directly from the New Testament (John 8:3-11). Some theologians and biblical scholars have speculated that Jesus was perhaps writing down the sins of the men who were about to stone her. Others note that Jesus' action recalls the One who gave the Law in the first place on Mount Sinai, for Exodus describes the Ten Commandments (including "You shall not commit adultery") being written in stone by the "finger of God". Therefore it is fitting that the One who gave the Law, now grants mercy. At any rate, it is from this incident we get the challenging words, "Let him who is without sin ... be the first to throw a stone at her" (John 8:7).
According to the Armenian Catholic tradition, this is true. Jesus was writing down the sins of those men, starting with the highest ranking members.
Gibson's Jesus begins writing in VERY LARGE letters, so He could not have written much, at least not without moving.
But my favorite answer to this perennial mystery came from an old Jesuit I know, who opined thus:
The Pharisees tell Christ that the woman was caught in the act of adultery (John 8:3-4) and they try to trip Him up by asking, "The Law of Moses says that she deserves stoning, but what do you say?" (John 8:5).
In answer, Christ bends down and writes something in the sand.
My Jesuit friend suspects that Christ wrote either Lev. 20:10 or Deut. 22:22, which is the Mosaic law to which the scribes were referring.
But those verses are quite explicit: If a woman and man commit adultery, they are both to be put to death.
Somehow or other, the Pharisees "caught" only the woman "in the act" of adultery. Very curious.
Or maybe the guy was a friend, and allowed to slip away.
The Jesuit's notion was that by being a "strict constructionist" on His Mosaic law, Christ was able to show mercy and forgiveness upon the woman.
Without her partner, what else could the scribes do, but put down their stones and walk away?
It also puts an edge to Christ's request/advice to her: "Go and sin no more." (Next time, you may not be so lucky.)
As I said, we will never know for sure in this life, but I like my Jesuit's explanation.