This is one of Wyeth's illustrations for Children Of the Bible. The tale it illustrates is curious. In Mark's account of the incident at Gethsemane, where Rabbi Jeshua was arrested by the Roman soldiers, there's a little aside about “a young man” dressed only in a sheet. When the soldiers tried to seize him they tore the sheet off and the young man fled naked into the night.
This is such an odd detail, and so scandalous, since nakedness was a real scandal in the culture of that time and place, that many scholars cite it as an example of something that must have been reliably reported from the earliest times and widely known, since no later chronicler would have included it otherwise.
According to Mark it was a cold night — so what was a kid doing out there dressed only in a sheet? No one knows, of course, but scholars have speculated that the young man (often identified as Mark himself) was sleeping in the house where the last supper was held, and seeing the rabbi and his disciples head off to Gethsemane, decided on an impulse to follow them.
That moment of impulse is clearly what Wyeth is depicting — in a dramatic tableau where the rabbi, touched by moonlight, walks off into darkness.
[With thanks to PZ for illuminating the incident, and to Golden Age Comic Book Stories for the Wyeth illustration. The painting above, by Gérard Douffet, from around 1620, clearly owes a lot to Caravaggio's masterpiece The Taking Of Christ, painted about 20 years earlier and a far greater work.]