Belief in God is rational.
Everything has a cause. So unless there is a first cause, then you would have an infinite regress. And then nothing could exist. Therefore there must be a first cause. Therefore God, the first cause, exists. QED. (You could prove the first step a priori that everything has a cause by noting that nothing can come from nothing. This makes it a priori, not just an empirical observation).
Since it is clear that the Rambam holds the פטור of מתעסק בשבת is because מלאכת מחשבת אסרה תורה then how does he understand Abyee in Sanhedrin 62b? Abyee says one who bows down to a statue and he did not know it is an idol לא כלום הוא