Is professing verbal belief in Jesus Christ worth nothing, in itself, given what Jesus said to many who believed on him in John 8:30?

As Jesus continued his discourse, where many believed on him, he then goes on to say their father is the devil! It ends up with those very ones trying to stone him. ***Is there a contradiction between this verse 30…*** *“And as he spake these words, many believed on him”* ***and verse 59***, “*Then took they up stones to cast at him:* but Jesus hid himself, and went out of the temple, going through the midst of them, and so passed by.” Or is it fair to say that Jesus’ discourse went on to expose a proud assumption, and false pride on their part, which betrayed they had no heart-felt belief? I ask this due to what Jesus said in ***verse 31***, *“Then said Jesus to those Jews which believed on him, If ye continue in my word, then are ye my disciples indeed.”* Are the words Jesus then went on to speak designed to expose what was really in their hearts, as to whether that contradicted their professed belief in him? **I seek clarification from those who maintain there is a need for confession with the mouth that has sprung from heart-felt repentance, as opposed to those who might think a public confession of faith *comes first*, and is effectively viewed by them as the most important aspect of becoming a Christian.**