9 “Then went in also that other disciple who had come first to the sepulchre.” He came first, and entered last. This also of a certainty is not without a meaning, but I am without the leisure needful for its explanation. “And he saw, and believed.” Here some, by not giving due attention, suppose that John believed that Jesus had risen again; but there is no indication of this from the words that follow. For what does he mean by immediately adding, “For as yet they knew not the scripture, that He must rise again from the dead”?
He could not then have believed that He had risen again, when he did not know that it behooved Him to rise again. What then did he see? What was it that he believed? What but this, that he saw the sepulchre empty, and believed what the woman had said, that He had been taken away from the tomb? “For as yet they knew not the scripture, that He must rise again from the dead.” Thus also when they heard of it from the Lord Himself, although it was uttered in the plainest terms, yet from their custom of hearing Him speaking by parables, they did not understand, and believed that something else was His meaning. But we shall put off what follows till another discourse.
Source: Tractates on the Gospel of John (New Advent)