John 12:44 - Matthew Poole's English Annotations on the Holy Bible

The words, at first view, seem to contain a contradiction, and denying the same act as to the same person; as if any man could believe, and yet not believe on Christ; but there is nothing less in them. By the same figurative way of speaking God tells the prophet Samuel, 1 Samuel 8:7, the people had not rejected Samuel, (that is, not Samuel alone), but they had rejected him. So Mark 9:37, Whosoever receiveth me, receiveth not me, (that is, not me alone), but him that sent me. So 1 Thessalonians 4:8. Or else thus, He that believeth on me, doth not believe on a mere man, as I appear at present to the world, but he also believeth on God that sent me. The Jews owned one God the Father, and acknowledged him the object of their faith, 1 Thessalonians 14:1, Ye believe in God; but they were blinded as to Christ, appearing only in the form of a man. So that our Saviour again by these words asserts his Divine nature, his oneness and equality with his Father; so as he was also the object of their faith, as well as his Father.