John Chrysostom — as excerpted in the Catena Aurea on John 1:35-36

“(Hom. xviii. [al. xvii.] c. 2) But wherefore went he not all about, preaching in every place of Judæa; instead of standing near the river, waiting for His coming, that he might point Him out? Because he wished this to be done by the works of Christ Himself. And observe how much greater an effort was produced; He struck a small spark, and suddenly it rose into a flame. Again, if John had gone about and preached, it would have seemed like human partiality, and great suspicion would have been excited. Now the Prophets and Apostles all preached Christ absent; the former before His appearance in the flesh, the latter after His assumption. But He was to be pointed out by the eye, not by the voice only; and therefore it follows: And looking upon Jesus us He walked, he saith, Behold the Lamb of God!”