The Bible declares that there are some people whose "faith" is on an equal level (or worse) than that of demons. "You believe that there is one God. Good! Even the demons believe that—and shudder." (James 2:19)
The faith of demons is but a mere belief in God's existence, not trusting in Christ to save them from sin (since Jesus never served as a mediator for demons), so there is no mystery that people with such faith are not justified.
True saving faith is a faith granted by God in which a person seeing the darkness of his own sin, casts aside his own righteousness, and trusts in the Savior to rescue him from God's wrath on account of his sin. Such Spirit-wrought faith binds us to Christ so that, in union with him, we participate in his righteousness, resting on the assurance of his mercy.
When people, by God's grace, desire to be saved from sin it reveals they no longer have a love for it and want to be out from under its' tyranny, so seeing they cannot save themselves, they turn to Christ to rescue them from it. As such, they will not be fruitless believes, but because the Lord implants a new love of righteousness within, they will exhibit their faith by following and obeying their Master, Jesus Christ.