Albert Barnes Commentary John 8:47

"He that is of God heareth the words of God: for this cause ye hear [them] not, because ye are not of God." — John 8:47 (ASV)

He that is of God. He that loves, fears, and honors God.

Heareth God's words. He listens to, or attends to the doctrines or commandments of God, as a child who loves his parent will regard and obey his commandments. This is evidence of true piety. A willingness to receive all that God teaches us, and to obey all his commandments, is an undoubted proof that we are his friends (John 14:21; 1 John 2:4; 1 John 3:24).

As the Jews did not show a readiness to obey the commands of God, it proved that they were not of him, and this was the reason for their rejection of the Lord Jesus.