There are many people who “believe in God,” but that doesn’t mean that they are all going to Heaven. The Bible says in James chapter two, in verse nineteen, that demons believe in God, and they even tremble at the thought of God. The demons were once angels that were made by the all-powerful God. The demons once worshipped and served God. They know where He sits on His throne, and they know of His power, His authority, His wisdom, His majesty, and that He controls everything.
It’s possible that Satan deceived the angels into following him by asking them, “Aren’t you tired of God controlling you and telling you what to do?” Obviously, we don’t know how the devil coerced them into following him. Even though Satan now controls the demons and tells them what to do, they still believe in God, and they still tremble at the thought of standing before God and being cast into the Lake of Fire for all eternity.
A belief in God that does not change the way that you live is useless. (Even small children who believe in Santa Claus will change the way they live for a month.) In fact, if your belief in God does not change the way that you live, then you’re living like an atheist. Or a demon.
The real question is not about “if” you believe in God, but have you accepted His Son, Jesus Christ, as your personal Savior and Lord? Jesus will change your life when you confess your sin and ask Him to forgive you of your sin.
If you believe in God, you will not only live like Jesus, but you will live for Jesus.