Did both men crucified with Jesus mock him, or only one?

Jesus hung on the cross for several hours, until the ninth hour (Mark 15:34), and much could change in that time. Matthew and Mark describe the early part of it, when passers-by and the chief priests and scribes all joined in the mockery (Matthew 27:39–43; Mark 15:29–31). Both use the Greek imperfect ōneidizon, ‘they were reproaching him’, which describes what was going on at that stage, not necessarily until the end.

Luke describes a later moment, when one of the two had stopped and turned on his companion: “Dost not thou fear God, seeing thou art in the same condemnation?” (Luke 23:40). So both accounts can be true. At first both men joined in the abuse; later one of them, having watched how Jesus suffered and heard him pray “Father, forgive them; for they know not what they do” (Luke 23:34), changed his mind. Barnes gives this explanation, and Gill allows it.

A plural for a singular

Augustine, and later Gill, suggested that Matthew and Mark, telling the story briefly, used the plural ‘the thieves’ where only one of them spoke, a common way of speaking. Augustine compared Hebrews 11:33, where ‘they’ stopped the mouths of lions, though Daniel alone is meant.

Some early manuscripts, among them Codex Vaticanus and Codex Bezae, lack the prayer “Father, forgive them” (Luke 23:34), though most have it. The explanation above does not rest on that one saying: the penitent thief had watched all that Jesus said and suffered on the cross.