Many commentaries try to determine what Jesus wrote on the ground as if after two thousand years something would still be left in the dust to decipher. However, in the Greek text, the emphasis is not on what he wrote but on his finger. Of the 613 commandments God gave to Moses, 603 were written on parchment with the pen of a man, the other ten were inscribed onto tablets of stone with the very finger of God (Exodus 31:18; Deuteronomy 9:10). One of the ten commandments was the law against adultery. The emphasis on the finger implies that Jesus, as the Author of this commandment, knew exactly all that the Mosaic Law said about the sin of adultery and its punishment.
The Law does not only state that anyone guilty of adultery must be stoned to death, but it also said that no one could be executed except at the testimony of two or three witnesses. Furthermore, those witnesses must not be guilty of the same sin as the accused and should be the ones to cast the first stone.
The Messiah’s statement here had nothing to do with being sinless or being judgmental. His point was that, if they were to judge this woman based on the Law, then everything the Law said about the sin of adultery must be considered. So let the witnesses who have not committed the sin of adultery themselves come forward and cast the first stone. Yet, one by one, the men walked away, showing that, at least among the witnesses, not one person was innocent of adultery.