A few times scripture point blank says what we read in John 3:15, “That whosoever believeth in him should not perish, but have eternal life.” Another instance is John 3:36, “He that believeth on the Son hath everlasting life: and he that believeth not the Son shall not see life; but the wrath of God abideth on him.” Believing in Jesus Christ is not mere intellectual assent to facts about who Jesus is.
True, it matters what you think about Jesus, that you get it right. That is part of belief, but it is not all. You know this: some people will say they believe in Jesus Christ and that “belief” shows up barely to nothing.
In John 3:36, the first word “believeth” is the most common word for “belief,” the Greek pisteuo. However, in the second half, “believeth” is another word, peitho, which is translated elsewhere, “obey” or “commit.” Genuine belief requires not just assent to facts, but also commitment. In other words, true faith is intellectual and volitional (involving the will), as well as emotional.
Part of the knowledge for faith is that Jesus must be Jesus. If He is actual Jesus, then He is better and higher than other things. He isn’t Jesus if that means essentially that He is something like fifth or sixth place to you.
And then, maybe He is Jesus, number one in your mind, but not first with your will. You’re not committed to Him. As a part of a description of this, it’s like putting Jesus on a shelf with all your other gods, something a Hindu might do. God wants more from you than mere acknowledgment of Him. He wants your seeking Him with your whole heart. That is genuine faith.