The difference between real faith and false faith in regards to believing in Jesus is the difference between belief in who Jesus is, God in flesh (John 1:1,14) and that he bore our sins in his body and the cross (1 Peter 2:24) and an intellectual belief that he lived and died.  Real faith is trust in what Christ has done on the cross as a sacrifice for sins, versus false faith which is believing that Jesus simply died the same as anyone else might die. It’s the difference between what is called ascentia and fiducia. Ascentia is mental assent, an intellectual acknowledgment of something.  For example, the devil believes that God exists (James 2:19), but does not trust in God and his wisdom.  However, with fiducia there is not only a mental acknowledgment of something, but the person also believes in its actuality, its meaning, and its validity. So for example, Christians truly believe in the deity of Christ and in His sacrifice for our sins.  Christians put their trust in the work of Christ to save us from our sins. Unbelievers do not do that.

Another form of false faith is believing in Jesus as someone he is not. For example, the Church of Jesus Christ of Latter-day Saints, the Mormons, believes that Jesus is literally the brother of all people because we all pre-existed and Jesus was the first one born to God and his goddess wife. They also believe that their God came from another planet. Therefore, their faith, though sincere, is misplaced and is equivalent to a false faith. So, faith is only as good as who you put it in. If you were to put your faith into something false, then it is false faith. It does not matter how sincere a person is when it is in something false.

False faith in Christ would also be “believing” in him with the wrong motives. For example, someone might believe and “trust in Christ” because he expects that Jesus will provide more money for his bank account, or so that he can get something of material value. This is not a proper faith in Christ. It is a misplaced faith because it’s not in agreement with what Jesus came to do which was to die for our sins, not provide us cash and possessions.

For the most part, true faith in Christ means trusting that he is God in flesh (John 1:1, 14; Colossians 2:9), that he died on the cross for our sins (1 Peter 2:24), and that he physically rose from the dead (1 Corinthians 15:1-4). We trust and what he has done and by faith receive his sacrifice for our spiritual (Romans 5:1; John 1:12). This is what it means to have real faith in Christ as opposed to false faith.