Albert Barnes Commentary John 12:44

"And Jesus cried and said, He that believeth on me, believeth not on me, but on him that sent me." — John 12:44 (ASV)

Jesus cried and said. John does not say where or when this was; it is probable, however, that it was a continuation of the discourse recorded in John 12:30-36. Jesus saw their unbelief, and proceeded to state the consequence of believing on him, and of rejecting him and his message.

Believeth not on me. That is, not on me alone, or his faith does not terminate on me. Compare to Matthew 10:20; Mark 9:37. It involves, also, belief in him that sent me. Jesus uniformly represents the union between himself and God as so intimate that there could not be faith in him unless there was also faith in God. He did the same works (John 5:17–20, 36; John 10:25, 37), and taught the very doctrine which God had commissioned him to do, John 8:38; John 5:30, 20-23.