16 What sort of a man this Nathanael was, we prove by the words which follow. Hear what sort of a man he was; the Lord Himself bears testimony. Great is the Lord, known by the testimony of John; blessed Nathanael, known by the testimony of the truth. Because the Lord, although He had not been commended by the testimony of John, Himself to Himself bore testimony, because the truth is sufficient for its own testimony. But because men were not able to receive the truth, they sought the truth by means of a lamp, and therefore John was sent to show them the Lord. Hear the Lord bearing testimony to Nathanael: “Nathanael said unto him, Can any good thing come out of Nazareth? Philip says to him, Come and see. And Jesus sees Nathanael coming to Him, and says concerning him, Behold an Israelite indeed, in whom is no guile.” Great testimony! Not of Andrew, nor of Peter, nor of Philip was that said which was said of Nathanael, “Behold an Israelite indeed, in whom is no guile.”
Source: Tractates on the Gospel of John (New Advent)