“Faith” by itself is meaningless. No one just has “faith”. “Faith” has to be in something. So, to speak intelligently of faith, we must speak both of the act of believing, and in the thing believed. People believe things. They don’t just “believe”.
According to the Scripture, “saving faith” does not save because it is faith, like somehow there is something about the act of believing that causes a person to be saved. What saves about “saving faith” is the thing believed.
And, according to Scripture, what is the thing believed? The “thing believed” is not that God exists. Common sense, not faith, will tell a person that God exists. Obviously God exists, or we wouldn’t be here to ponder that. But God has also spoken. And not just spoken, either. He has said some remarkable things, things which we could never have known, could never have guessed, things which the human mind could never, on its own, imagine.
The Gospel is such a thing that God has spoken. It is a remarkable thing. It is a “thing to be believed”. It is a promise from God, that He will save those who believe it. Faith doesn’t save; God saves. And Saving Faith is not “believing in God”; it is believing God. God promises to save those who trust that Jesus is their Savior. Why should anyone believe that? Because God has said so. Believe Him! And you will be saved!