Excerpt from ‘Bible Truths Explained: Faith’.
Millions of people claim to believe in Christ—but the faith they possess is not true faith. Their faith is in the religion to which they belong, and to its teachings, rather than in the Person and redemptive work of Christ as revealed to us in the Bible. The faith of which the Bible speaks is associated only with those whom the Holy Spirit has regenerated. Faith in any religion that differs from the teaching of the Bible is not genuine God-given faith. Similarly, the demons have faith. They believe in Christ—and tremble at the prospect of their final doom. Their faith—which although based on a clear knowledge of the truth—differs fundamentally from true faith. They are utterly convinced of the consequences of their sin and of their final judgement. However, their complete faith or belief in their eternal destiny can never be associated with their salvation—for there is no possibility of salvation for the devil and his (fallen) angels. So it is with all those who do not possess true spiritual and God-given faith, or who place their entire confidence in any form of truth that is different from the Word of God—the Bible.
Matthew 7:21-23 KJV
(21) Not every one that saith unto me, Lord, Lord, shall enter into the kingdom of heaven; but he that doeth the will of my Father which is in heaven. (22) Many will say to me in that day, Lord, Lord, have we not prophesied in thy name and in thy name have cast out devils? and in thy name done many wonderful works? (23) And then will I profess unto them, I never knew you: depart from me, ye that work iniquity. (See vv.13-20)
(Read or download the full version of ‘Bible Truths Explained: Faith’ from the relevant section of this website.)