3. The efficacy of prayer, so far from being inconsistent with, is founded on, the immutability of the Divine purposes and the faithfulness of the Divine promises. God's purposes are justly held, in all other cases, to include the _means_ as well as the _ends_; and they are often fulfilled through the instrumentality of "second causes." His purpose to provide for the wants of man and beast has reference not merely to the harvest which is the result, but also to the agricultural labor by which, instrumentally, the harvest is prepared. May not "prayer" be also _a means_ ordained by God in the original constitution of the world, a means towards certain ends which are made dependent on its use? If it be such a means, then its "efficacy" is established, in the only sense in which we are concerned to contend for it; while it is shown to be _no more inconsistent_ with the immutability of the Divine purposes, than any other system of _means or instruments_ that may be employed as subordinate agencies in the government of the world. This important view is strikingly illustrated in Scripture. For some of the _purposes_ of God, which might have been undiscoverable in the mere light of Nature, are there explicitly declared; nay, they are thrown into the form of express _promises_, to which the Divine faithfulness is solemnly pledged; and yet the exercise of prayer, so far from being superseded by these promises, is rather stimulated and encouraged by them; and the believer pleads with increased fervor and confidence when he simply converts _God's promises into his own petitions_. He feels that in doing so he is taking God at his word; and that his own prayer, in so far as it is warranted by His promise, cannot be ineffectual any more than God's faithfulness can fail.