Albert Barnes Commentary John 3:34

"For he whom God hath sent speaketh the words of God: for he giveth not the Spirit by measure." — John 3:34 (ASV)

Whom God has sent. The Messiah.

Speaks the words of God. The truth, or commands of God.

For God gives not the Spirit. The Spirit of God. Though Jesus was God as well as man, yet, as Mediator, God anointed him, or endowed him with the influences of his Spirit, so as to be completely qualified for his great work.

By measure. Not in a small degree, but fully, completely. The prophets were inspired on particular occasions to deliver special messages. The Messiah was continually filled with the Spirit of God. "The Spirit dwelt in him, not as a vessel, but as in a fountain, as in a bottomless ocean" (Henry).