Of course, God intervenes in history as He sees fit, with or without our prayers. But insofar as God’s will is that we participate in the unfolding of His plan (which we call ‘Providence’) by the action of our will, under our own freedom (which is his great gift to us, as it differentiates us from the beasts), we increase the good in the world through prayer, and we increase the evil in the world through a lack of prayer, or an antipathy toward it.