Bruce Ware, “Prayer and the Sovereignty of God,” in For the Fame of God’s Name:
Clearly, God does not need us to bring our concerns to him in order for him to know what we need or to know how best to act. He is God! He knows perfectly our backgrounds, our families, our friends, our circumstances, our jobs, our relationships, our struggles, our difficulties, our needs, our desires, our fears, our dreams, our longings, our strengths, our weaknesses, our successes, our failures, our sins, and everything else, both internal and external, related to our lives. He doesn’t need us to pray. He doesn’t learn anything when we do. He isn’t helped in knowing better what course of action to take. The fact is, nothing that we are or have or give can benefit God in any respect whatsoever, and our prayers are no exception. Therefore, God’s purpose in instituting prayer, and in longing for us to pray, simply cannot have anything to do with helping him.
Rather, one of the most startling and wondrous realizations that any Christian can have is that much of the purpose of prayer has to do with one simple thing: relationship — that is, relationship coram Deo (before the face of God). One great and glorious reason God devised prayer was to use it as a mechanism to draw us to himself, to help us see how much we need him, to set before us constantly the realization that he is everything we are not, and he possesses everything that we lack. We are weak, but he is strong; we are foolish, but he is wise; we are untrustworthy, but he is faithful; we are ignorant, but he is infinitely knowledgeable; we are poor and empty, but he is rich and full. Imagine this: although God does not need any of what we bring to him in prayer, he longs for us to bring everything that we do bring to him and so much more! He wants us to pray without ceasing (1 Thess. 5:17), in part because our need for him never ceases. Prayer is not instituted, then, as a means of helping God out. Just the opposite: it is for our sake, and for ours alone.