John Lightfoot on John 3:31

[He that is of the earth is earthly.] Mark but the antithesis, and you will not suspect any tautology:

1. He that is of the earth, and He that cometh from heaven. Where the antithesis is not so much between Christ and John, as betwixt Christ and all mankind.

2. He is of the earth, and He is above all. He that is of the earth is only of earthly degree, or rank: and he that is from heaven is above all degree.

3. He speaks of the earth, and what he hath seen and heard, that he testifieth. He that is of the earth speaketh earthly things, and what he hath learned upon the earth; but he that is from heaven speaketh those things which he learned in heaven, viz., those things which he hath seen and heard from God. The Baptist seems to allude to the manner of bearing witness, and teaching. In matter of fact there was need of an eyewitness; in matter of doctrine, they delivered what they had heard from their Master.