ISAIAH has often been called the evangelical prophet, for the wonderful clearness with which he announces the coming Redeemer, both in His humiliation and suffering, and in the glory of the kingdom He was to establish. And yet it was given to Jeremiah, in this passage, and to Ezekiel, in the parallel one, to foretell what would actually be the outcome of the Redeemer's work and the essential character of the salvation He was to effect, with a distinctness which is nowhere found in the older prophet. In words which the New Testament (Hebrews viii.) takes as the divinely inspired revelation of what the New Covenant is of which Christ is the Mediator, God's plan is revealed and we are shown what it is that He will do in us, to make us fit and worthy of being the people of which He is the God. Through the whole of the Old Covenant there was always one trouble: man's heart was not right with God. In the New Covenant the evil is to be remedied. Its central promise is a heart delighting in God's law and capable of knowing and holding fellowship with Him. Let us mark the fourfold blessing spoken of.
1. "I will put My law in their inward parts, and write it in their hearts." Let us understand this well. In our inward parts, or in our heart, there are no separate chambers in which the law can be put, while the rest of the heart can be given up to other things; the heart is a unity. Nor are the inward parts and the heart like a house, which can be filled with things of an entirely different nature from what the walls are made of, without any living organic connection. No; the inward parts, the heart, are the disposition, the love, the will, the life. Nothing can be put into the heart, and especially by God, without entering and taking possession of it, without securing its affection and controlling its whole being. And this is what God undertakes to do in the power of His divine life and operation, to breathe the very spirit of His law into and through the whole inward being. "I will put it into their inward parts, and write it in their hearts." At Sinai the tables of the Covenant, with the law written on them, were of stone, as a lasting substance. It is easy to know what that means. The stone was wholly set apart for this one thing -- to carry and show this Divine writing. The writing and the stone were inseparably connected. And so the heart in which God gets His way, and writes His law in power, lives only and wholly to carry that writing, and is unchangeably identified with it. So alone can God realise His purpose in creation, and have His child of one mind and one spirit with Himself, delighting in doing His will. When the Old Covenant with the law graven on stone had done its work in the discovering and condemning of SIN, the New Covenant would give in its stead the life of obedience and true holiness of heart. The whole of the Covenant blessing centres in this -- the heart being put right and fitted to know God: "I will give them an heart to know Me, that I am the Lord; and they shall be My people, and I will be their God; for they shall return unto Me with their whole heart" (Jer. xxiv.7).
2. "And I will be their God, and they shall be My people." Do not pass these words lightly. They occur chiefly in Jeremiah and Ezekiel in connection with the promise of the everlasting Covenant. They express the very highest experience of the Covenant relationship. It is only when His people learn to love and obey His law, when their heart and life are together wholly devoted to Him and His will, that He can be to them the altogether inconceivable blessing which these words express, "I will be your God." All I am and have as God shall be yours. All you can need or wish for in a God, I will be to you. In the fullest meaning of the word, I, the Omnipresent, will be ever present with you, in all My grace and love. I, the Almighty One, will each moment work all in you by My mighty power. I, the Thrice-Holy One, will reveal My sanctifying life within you. I will be your God. And ye shall be My people, saved and blessed, ruled and guided and provided for by Me, known and seen to be indeed the people of the Holy One, the God of glory. Only let us give our hearts time to meditate and wait for the Holy Spirit to work in us all that these words mean.
3. "And they shall teach no more every man his neighbour, and every man his brother, saying, Know the Lord, for they shall all know Me, from the least of them unto the greatest of them, saith the Lord." Individual personal fellowship with God, for the feeblest and the least, is to be the wonderful privilege of every member of the New Covenant people. Each one will know the Lord. That does not mean the knowledge of the mind, -- that is not the equal privilege of all, and that in itself may hinder the fellowship more than help it, -- but with that knowledge which means appropriation and assimilation, and which is eternal life. As the Son knew the Father because He was one with Him and dwelt in Him, the child of God will receive by the Holy Spirit that spiritual illumination which will make God to him the One he knows best, because he loves Him most and lives in Him. The promise, "They shall be all taught of God," will be fulfilled by the Holy Spirit's teaching. God will speak to each out of His Word what he needs to know.
4. "For I will forgive their iniquities, and I will remember their sin no more." The word for shows that this is the reason of all that precedes. Because the blood of this New Covenant was of such infinite worth, and its Mediator and High Priest in heaven of such Divine power, there is promised in it such a Divine blotting out of sin that God cannot remember it. It is this entire blotting out of sin that cleanses and sets us free from its power, so that God can write His law in our hearts, and show Himself in power as our God, and by His Spirit reveal to us His deep things -- the deep mystery of Himself and His love. It is the atonement and redemption of Jesus Christ wrought without us and for us, that has removed every obstacle and made it meet for God, and made us meet, that the law in the heart, and the claim on our God, and the knowledge of Him, should now be our daily life and our eternal portion.
Here we now have the Divine summary of the New Covenant inheritance. The last-named blessing, the pardon of sin, is the first in order, the root of all. The second, having God as our God, and the third, the Divine teaching, are the fruit. The tree itself that grows on this root, and bears such fruit, is what is named first -- the law in the heart. 
The central demand of the Old Covenant, Obey My voice, and I will be your God, has now been met. With the law written in the heart, He can be our God, and we shall be His people. Perfect harmony with God's will, holiness in heart and life, is the only thing that can satisfy God's heart or ours. And it is this the New Covenant gives in Divine power, "I will give them an heart to know Me; and I will be their God, and they shall be My people; for they shall turn to Me with their whole heart." It is on the state of the heart, it is on the new heart, as given by God, that the New Covenant life hinges.
But why, if all this is meant to be literally and exactly true of God's people, why do we see so little of this life, experience so little in ourselves? There is but one answer: Because of your unbelief! We have spoken of the relation of God and man in creation as what the New Covenant is meant to make possible and real. But the law cannot be repealed that God will not compel. He can only fulfil His purpose as the heart is willing and accepts His offer. In the New Covenant all is of faith. Let us turn away from what human wisdom and human experience may say, and ask God Himself to teach us what His Covenant means. If we persevere in this prayer in a humble and teachable spirit, we can count most certainly on its promise: "They shall no more every man teach his neighbour: Know the Lord, for they shall all know Me." The teaching of God Himself, by the Holy Spirit, to make us understand what He says to us in His Word, is our Covenant right. Let us count upon it. It is only by a God-given faith that we can appropriate these God-given promises. And it is only by a God-given teaching and inward illumination that we can see their meaning, so as to believe them. When God teaches us the meaning of His promises in a heart yielded to His Holy Spirit, then alone we can believe and receive them in a power which makes them a reality in our life.
But is it really possible, amid the wear and tear of daily life, to walk in the experience of these blessings? Are they really meant for all God's children? Let us rather ask the question, Is it possible for God to do what He has promised? The one part of the promise we believe -- the complete and perfect pardon of sin. Why should we not believe the other part -- the law written in the heart, and the direct Divine fellowship and teaching? We have been so accustomed to separate what God has joined together, the objective, outward work of His Son, and the subjective, inward work of His Spirit, that we consider the glory of the New Covenant above the Old to consist chiefly in the redeeming work of Christ for us, and not equally in the sanctifying work of the Spirit in us. It is owing to this ignorance and unbelief of the indwelling of the Holy Spirit, as the power through whom God fulfils the New Covenant promises, that we do not really expect them to be made true to us.
Do let us turn our hearts away from all past experience of failure, as caused by nothing but unbelief; do let us admit fully and heartily, what failure has taught us, the absolute impossibility of even a regenerate man walking in God's law in his own strength, and then turn our hearts quietly and trustfully to our own Covenant God. Let us hear what He says He will do for us, and believe Him; let us rest on His unchangeable faithfulness and the surety of the Covenant, on His Almighty power and the Holy Spirit working in us; and let us give up ourselves to Him as our God. He will prove that what He has done for us in Christ is not one whit more wonderful than what He will do in us every day by the Spirit of Christ.
 On the law written in the heart, see Note B.