Matthew 26:65 - Ellicott's Commentary On The Whole Bible

Then the high priest rent his clothes. — The act was almost as much a formal sign of condemnation as the putting on of the black cap by an English judge. The judges in a Jewish trial for blasphemy were bound to rend their clothes in twain when the blasphemous words were uttered, and the clothes so torn were never afterwards to be mended. In Acts 14:14 the same act appears, on the part of Paul and Barnabas, as the expression of an impulsive horror, as it had done of old when Eliakim rent his clothes on hearing the blasphemies of Rabshaken (2 Kings 18:37). A comparison of the Greek word here and in Mark 14:63 shows that it included the tunic or under-garment as well as the cloak.