Today many people say the believe in Jesus, but often that is a Jesus made in thier own image, not Jesus as he reveals Himself ot us in the Bible. In John 8:31-59 we see that the people in Jesus day also did the same thing, they said they believed in Jesus, but on their own terms, with their own ideas.
Jesus confronts the people of his day who bought their own ideas about Jesus to the table and said that if you wanted true freedom, true life, to truly live in God's family then you needed to trust Jesus as He reveals himself.
Believing in Jesus and doing what he says is the road to true freedom anything else, Jesus says, is living as a child of Satan!