John Chrysostom — as excerpted in the Catena Aurea on John 1:47-51

“(Hom. xxi. [al. xx.] 1) Many when they read this passage, are perplexed at finding that, whereas Peter was pronounced blessed for having, after our Lord’s miracles and teaching, confessed Him to be the Son of God, Nathanael, who makes the same confession before, has no such benediction. The reason is this. Peter and Nathanael both used the same words, but not in the same meaning. Peter confessed our Lord to be the Son of God, in the sense of very God; the latter in the sense of mere man; for after saying, Thou art the Son of God, he adds, Thou art the King of Israel; whereas the Son of God was not the King of Israel only, but of the whole world. This is manifest from what follows. For in the case of Peter Christ added nothing, but, as if his faith were perfect, said, that he would build the Church upon his confession; whereas Nathanael, as if his confession were very deficient, is led up to higher things: Jesus answered and said unto him, Because I said unto thee, I saw thee under the fig tree, believest thou? Thou shalt see greater things than these. As if He said, What I have just said has appeared a great matter to thee, and thou hast confessed Me to be King of Israel; what wilt thou say when thou seest greater things than these? What that greater thing is He proceeds to shew: And He saith unto him, Verily, verily, I say unto you, Hereafter ye shall see heaven open, and the angels of God ascending and descending upon the Son of man. See how He raises him from earth for a while, and forces him to think that Christ is not a mere man: for how could He be a mere man, whom angels ministered to? It was, as it were, saying, that He was Lord of the Angels; for He must be the King’s own Son, on whom the servants of the King descended and ascended; descended at His crucifixion, ascended at His resurrection and ascension. Angels too before this came and ministered unto Him, and angels brought the glad tidings of His birth. Our Lord made the present a proof of the future. After the powers He had already shewn, Nathanael would readily believe that much more would follow.”