This spake he, signifying by what death he should glorify God. — These words are a comment by the writer, and quite in St. John’s style. (Comp. John 2:21; John 6:6; John 7:39; John 12:33.)
“By what death,” or, more exactly, by what manner of death (comp. John 12:33; John 18:32), indicates generally the martyrdom of Peter as distinct from a natural death, without special reference to the crucifixion. (See Note on last verse.)
For the phrase “glorify God,” comp. John 13:31; John 17:1; and see also Philippians 1:20; 1 Peter 4:16. From its occurrence here in connection with St. Peter, it passed into the common language of the Church for the death of martyrs.
Follow me. — It may be, and the next verse makes it probable, that our Lord withdrew from the circle of the disciples, and by some movement or gesture signified to Peter that he should follow Him; but these words must have had for the Apostle a much fuller meaning. By the side of that lake he had first heard the command “Follow Me” (Matthew 4:19); when sent forth on his apostleship, he had been taught that to follow Christ meant to take up the cross (Matthew 10:38); it was his words which drew from Christ the utterance, “If any man will come after Me, let him deny himself, and take up his cross and follow Me” (Matthew 16:23); to his question at the Last Supper came the answer, “Whither I go, thou canst not follow Me now; but thou shalt follow Me afterwards” (John 13:36); and now the command has come again with the prophecy of martyrdom, and it must have carried to his mind the thought that he was to follow the Lord in suffering and death itself, and through the dark path which He had trodden was to follow Him to the Father’s home.