If you believe that the universe exists, in some sense, inside of God --for instance, in God's mind --then it's not incompatible to simultaneously believe that God did something, that it proceeded from entirely naturalist causes, and that also it proceeded from human will. The metaphor I prefer for this is a writer writing a book. If the book is well-written, everything that happens in the book will happen for reasons that are consistent and explainable with the framework of the story. But ultimately, it is the author that makes things happen. Given that scenario, does it make sense for the character to try to commune with the author? If every character is equally a creation of the author, and if the author is committed to the internal realism of the narrative, then it what sense is it an advantage for a character to reach out to the author?
Possible answers (a) the character finds it psychologically beneficial to contemplate the author, (b) there's no guarantee that the author will always respect realism (c) it is possible (i.e. one cannot rule out the possibility that) that the author can find a way to intervene in the story on behalf of the character that either does respect realism or apparently does so.
The higher level question is then, why do both? Why both trust in God and in your own efficacy? Or, conversely, why does God act both directly, and through us? We may not be able to answer the second question, from God's perspective, but we can craft an answer to the first. First, in order to be personally aligned with God and God's will (see Esther 4:13 and Ezekiel 33: 1-9). In other words, God will do it with or without us, but it's better that God do it with us. Second, because human efficacy is limited, but God's is not. In other words, we try as hard as we can, and inevitably fall short, but God does not fall short. Therefore we pray AND act.