Jesus declared to the Jews, “You have neither heard His [God’s] voice at any time, nor seen His form.” Yet the voice of God was heard many times in the OT (cf. 1 Sam. 3:4-14), and the Father spoke from heaven three times during Jesus’ earthly ministry (Matt. 3:17; 17:5; John 12:28).
John 5:30 - 47
ESV - 30 I can do nothing on my own. As I hear, I judge, and my judgment is just, because I seek not my own will but the will of him who sent me. 31 If I alone bear witness about myself, my testimony is not deemed true.
For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.