The painting depicts a scene reported in St John's gospel (Joh 8,1-11): while Christ is teaching in the temple the scribes and pharisees bring him a woman who has been accused of adultery. They ask him how he intends to treat this case under Mosaic law, which commands the stoning of the adulteress (Dtn 22,23). They wish to tempt Christ with the question so they can institute proceedings against him. But Christ does not answer, instead he kneels down and writes something on the ground. As he rises he tells the accusers that whoever is without sin should throw the first stone. He kneels again to write on the ground. While he is doing this the scribes depart without throwing a stone at the woman.
Christ does not condemn the adulteress, but he warns her not to sin again.
[Susanne Wegmann, in Exhib. Cat. Wittenberg 2015, No. 3/40](translation, cda 2016)