John 3:34

Doth not give the Spirit by measure. Christ, even as man, has a plenitude of graces. See chapt. i. ver. 14. And all things, all creatures, both in heaven and earth, are given into his hands, and made subject to him, as man. See 1 Corinthians xv. 26. (Witham)

He who hath so believed the testimony of Christ, as to accept him, and to believe in him as his Saviour, hath, by that his believing, set to his seal that God, in all his promises of the Messiah under the Old Testament, is true; that a word hath not failed of whatsoever God hath there spoken of that nature. According to this is that 1Jn 5:10, He that believeth not God hath made him a liar; because he believeth not the record that God gave of his Son. This saying doth notably commend faith, and defame unbelief. Faith in Christ as the only true Mediator and Saviour, giveth testimony to the truth of God, and sealeth it. Unbelief defames God, and doth in effect say that God is a liar.

Verses 22-36 John was fully satisfied with the place and work assigned him; but Jesus came on a more important work. He also knew that Jesus would increase in honour and influence, for of his government and peace there would be no end, while he himself would be less followed. John knew that Jesus came from heaven as the Son of God, while he was a sinful, mortal man, who could only speak about the more plain subjects of religion. The words of Jesus were the words of God; he had the Spirit, not by measure, as the prophets, but in all fulness. Everlasting life could only be had by faith in Him, and might be thus obtained; whereas all those, who believe not in the Son of God, cannot partake of salvation, but the wrath of God for ever rests upon them.