Believed on him, in the sense before expressed. Our Saviour well enough saw their hearts, and in what manner they believed, and what sort of disciples they were, viz. only nominal: they have the name of disciples who come after Christ to hear him; but they are his disciples indeed, who make his doctrine the rule of their lives. He therefore tells them, That not a mere saying to him Lord, Lord, and yielding some light assent to some propositions of truth in the gospel, would make them his disciples in truth and reality, without an abiding and continuance in the words which he taught them.
Related Commentaries of John 8:31
John 8:31
31 Then said Jesus to those Jews which believed on him,If ye continue in my word, then are ye my disciples indeed;