John Chrysostom — as excerpted in the Catena Aurea on John 8:48-51

“(Hom. lv. 1) He says, keep, i. e. not by faith, but by purity of life. And at the same time too He means it as a tacit intimation that they can do nothing to Him. For if whoever keepeth His word, shall never die, much less is it possible that He Himself should die.”