“Anyone who runs ahead and does not continue in the teaching of Christ does not have God; whoever continues in the teaching has both the Father and the Son.” (II John 1:9)
If you are a true Christian you will “continue in the teaching of Christ.” This is because if you have truly believed and repented of your sins, then you are indwelt by the Holy Spirit. In fact, the Bible says that you are “born of the Spirit” (John 3:6). God Himself will keep you as His own, and no one will “snatch” you away from Him (John 10:28).
But some who believe the facts of the Bible intellectually are not real believers. They have not repented of their sins and have not believed in their hearts. They may later change their minds and decide that Jesus never died for the sins of the world or was raised from the dead. These people were never believers in the first place.