Question
Hi, I was wondering if I do a mitzvah without fully believing in God, does it mean anything? Or is it meaningless, or maybe even hypocrisy? I feel like starting to say the “Grace after Meals” blessings in Hebrew or English, but I’m not sure if it’s worthwhile since I don’t observe and believe everything at the moment. Thanks.

Question
In the Tanakh, there is a concept of the Holy Spirit. For example: "the spirit of God dwelled on David strongly". Is there the power of the Holy Spirit according to Judaism? Also, is there the power of the "evil spirit"?