There are two opposite ways of looking at the Old Testament with which this apostolic teaching is inconsistent, and which, by anticipation, it condemns.
There is the opinion of those who say that God's promises to His people in the Old Testament have not been fulfilled, and never will be. That is the opinion held by many among the modern Jews, who have renounced all that was most characteristic in the religion of their fathers, and attenuated it into the merest deistical film of a creed. It is the opinion also of many who study the Bible as a piece of literary antiquity, but get to no perception of the life which is in it, or of the organic connexion between the Old Testament and the New. What the Apostle says of his countrymen in his own time is true of both these classes--when they read the Scriptures, there is a veil upon their hearts. The Old Testament promises have been fulfilled, every one of them. Let a man be taught what they mean, not as dead letters in an ancient scroll, but as present words of the living God; and then let him look to Jesus Christ, the Son of God, and see whether there is not in Him the mighty, the perpetual confirmation of them all. We smile sometimes at what seems the whimsical way in which the early Christians, who had not yet a New Testament, found Christ everywhere in the Old; but though it may be possible to err in detail in this pursuit, it is not possible to err on the whole. The Old Testament is gathered up, every living word of it, in Him; we are misunderstanding it if we take it otherwise.
The opinion just described is a species of rationalism. There is another opinion, which, while agreeing with the rationalistic one that many of God's promises in the Old Testament have not yet been fulfilled, believes that their fulfilment is still to be awaited. If one might do so without offence, I should call this a species of fanaticism. It is the error of those who take the Jewish nation as such to be the subject of prophecy, and hope for its restoration to Palestine, for a revived Jerusalem, a new Davidic monarchy, even a reign of Christ over such an earthly kingdom. All this, if we may take the Apostle's word for it, is beside the mark. Equally with rationalism it loses the spirit of God's word in the letter. The promises have been fulfilled already, and we are not to look for another fulfilment. Those who have seen Christ have seen all that God is going to do--and it is quite adequate--to make His word good. He who has welcomed Christ knows that not one good word of all that God has spoken has failed. God has never, by the promises of the Old Testament, or by the instincts of human nature, put a hope or a prayer into man's heart that is not answered and satisfied abundantly in His Son.
But leaving the reference to the Old Testament on one side, it is well worth while for us to consider the practical meaning of the truth, that _all_ God's promises are Yea in Christ. God's promises are His declarations of what He is willing to do for men; and in the very nature of the case they are at once the inspiration and the limit of our prayers. We are encouraged to ask all that God promises, and we must stop there. Christ Himself then is the measure of prayer to man; we can ask all that is in Him; we dare not ask anything that lies outside of Him. How the consideration of this should expand our prayers in some directions, and contract them in others! We can ask God to give us Christ's purity, Christ's simplicity, Christ's meekness and gentleness, Christ's faithfulness and obedience, Christ's victory over the world. Have we ever measured these things? Have we ever put them into our prayers with any glimmering consciousness of their dimensions, any sense of the vastness of our request? Nay, we can ask Christ's glory, His Resurrection Life of splendour and incorruption--the image of the heavenly. God has promised us all these things, and far more: but has He always promised what we ask? Can we fix our eyes on His Son, as He lived our life in this world, and remembering that this, so far as this world is concerned, is the measure of promise, ask without any qualification that our course here may be free from every trouble? Had Christ no sorrow? Did He never meet with ingratitude? Was He never misunderstood? Was He never hungry, thirsty, weary? If all God's promises are summed up in Him--if He is everything that God has to give--can we go boldly to the throne of grace, and pray to be exempted from what He had to bear, or to be richly provided with indulgences which He never knew? What if all unanswered prayers might be defined as prayers for things not included in the promises--prayers that we might get what Christ did not get, or be spared what He was not spared? The spirit of this passage, however, does not urge so much the definiteness as the compass and the certainty of the promises of God. They are so many that Paul could never enumerate them, and all of them are sure in Christ. And when our eyes are once opened on Him, does not He Himself become as it were inevitably the substance of our prayers? Is not our whole heart's desire, Oh that I might win _Him_! Oh that _He_ might live in me, and make me what He is! Oh that _that_ Man might arise in me, that the man I am may cease to be! Do we not feel that if God would give us His Son, all would be ours that we could take or He could give?