John Gill Commentary John 1:34

"And I have seen, and have borne witness that this is the Son of God." — John 1:34 (ASV)

And I saw
The Spirit descending from heaven as a dove, and lighting upon Jesus, and remaining some time on him; this he saw with his bodily eyes:

and bore record ;
at the same time, before all the people that were with him, when he baptized Jesus:

that this is the Son of God ;
the natural, essential, and eternal Son of God; who being sent in the fulness of time, had assumed an human nature, in which he became subject to all ordinances, and had the Spirit without measure bestowed on him; and which was an evidence who he was, and of what he came about.