The New Covenant solves the issue of mankind's unfaithfulness exposed by the Old Covenant.

Yes the Old Covenant only exposed mankind's unfaithfulness but it made no provision to solve it. The purpose of the law was that it might reveal sin (Romans 3:20) and lead us to Christ. God never designed or intended the old covenant to provide the solution. The Old Covenant could never make any person holy, righteous or give Life.

Mankind actually believed and thought that they could obey and please God so God needed to show and prove to them that this was IMPOSSIBLE for them to do.

The old Covenant was broken because of their unfaithfulness. Now if God did not solve the issue of Mankind's unfaithfulness we would still be under the Old Covenant without any hope.

Now the God News is that God has completely dealt with and solved this problem. How you ask.

Look at these quotes from Andrew Murray

Let us listen to the words in which God's Word calls us to know, and worship, and trust our Covenant-keeping God it may be we shall find what we have been looking for: the deeper, the full experience of all God's grace can do in us. In our text Moses says: "Know therefore that the Lord thy God, He is God, the faithful God, which keepeth covenant with them that love Him." Hear what God says in Isaiah: "The mountains shall depart, and the hills be removed; but My kindness shall not depart from thee, neither shall My covenant of peace be removed, saith the Lord that hath mercy on thee." More sure than any mountain is the fulfillment of every Covenant promise. Of the New Covenant, in Jeremiah, God speaks: "I will make an everlasting covenant with them, that I will not turn away from them, to do them good; but I will put My fear in their hearts, that they shall not depart from Me." The Covenant secures alike that God will not turn from us, nor we depart from Him: He undertakes both for Himself and us.

This is nothing but the restoration of the original relation between God and the man He had made in His likeness. He was on earth to be the very image of God, because God was to live and to work all in him, and he to find his glory and blessedness in thus owing all to God. This is the exceeding glory of the New Covenant, of the Pentecostal dispensation, that by the Holy Spirit God could now again be the indwelling life of His people, and so make the promise a reality: "I will cause you to walk in My statutes." With God's presence secured to us every moment of the day---"I will not turn away from them"; with God's "fear put into our heart " by His own Spirit, and our heart thus responding to His holy presence; with our hearts thus made right with God, we can, we shall walk in His statutes, and keep His judgments.

And this is indeed the glory of the New Covenant, the glory that excelleth, that this provision has been made. In a way that no human thought could have devised, by a stipulation that never entered into any human covenant, by an undertaking in which God's infinite condescension and power and faithfulness are to be most wonderfully exhibited, by a supernatural mystery of Divine wisdom and grace, the New Covenant provides a guarantee, not only for God's faithfulness, but for man's too! And this in no other way than by God Himself undertaking to secure man's part as well as His own. Do try and get hold of this.

Here is the inmost secret of the New Covenant. It deals with the heart of man in a way of Divine power. It not only appeals to the heart by every motive of fear or love, of duty or gratitude. That the law also did. But it reveals God Himself, cleansing our heart and making it new, changing it entirely from a stony heart into a heart of flesh, a tender, living, loving heart, putting His Spirit within it, and so, by His Almighty Power and Love, breathing and working in it, making the promise true, "I will cause you to walk in My statutes, and ye shall keep My judgments." A heart in perfect harmony with Himself, a life and walk in His way---God has engaged in Covenant to work this in us. He undertakes for our part in the Covenant as much as for His own.

WE have here four titles given to our Lord. Jesus in connection with the New Covenant. He is Himself called a Covenant. The union between God and man, which the Covenant aims at, was wrought out in Him personally; in Him the reconciliation between the human and Divine was perfectly effected; in Him His people find the Covenant with all its blessings; He is all that God has to give, and is the assurance that it is given . . . . He is called the Messenger of the Covenant, because He came to establish and to proclaim it . . . . He is the Surety of the Covenant, not only because He paid our debt, but as He is Surety to us for God, that God will fulfil His part; and Surety for us with God, that we will fulfil our part . . . . And He is Mediator of the Covenant, because as the Covenant was established in His atoning blood, is administered and applied by Him, is entered upon alone by faith in Him, so it is experimentally known only through the power of His resurrection life, and His never-ceasing intercession. All these names point to the one truth, that in the New Covenant Christ is all in all.

A SURETY is one who stands good for another, that a certain engagement will be faithfully performed. Jesus is the Surety of the New Covenant. He stands surety with us for God--- that God's part in the Covenant will faithfully be performed. And He stands surety with God for us, that our part will be faithfully performed too. If we are to live in covenant with God, everything depends upon our knowing aright what Jesus secures to us. The more we know and trust Him, the more assured will our faith be that its every promise and every demand will be fulfilled, that a life of faithful keeping of God's Covenant is indeed possible, because Jesus is the Surety of the Covenant. He makes God's faithfulness and ours equally sure.

If you would be delivered from all this, learn ever to read the Book of the New Covenant in the New Covenant Spirit. One of the very first articles of the New Covenant has reference to this matter. When God says, I will put My law in their inward parts, and write it in their hearts, He engages that the words of His Holy Book shall no longer be mere outward teaching, but that what they command shall be our very disposition and delight, wrought in us as a birth and a life by the Holy Spirit. Every word of the New Covenant then becomes a Divine assurance of what may be obtained by the Holy Spirit's working. The soul learns to see that the letter killeth, that the flesh profiteth nothing. The study, and knowledge of, the delight in, Bible words and thoughts, cannot profit, except as the Holy Spirit is waited on to make them life. The acceptance of Holy Scripture in the letter, the reception of it in the human understanding, is seen to be as fruitless as was Israel's at Sinai. But as the Word of God, spoken by the Living God through the Spirit into the heart that waits on Him, it is found to be quick and powerful. It then is a word that worketh effectually in them that believe, giving within the heart the actual possession of the very grace of which the Word has spoken.

If we have at all understood the teaching of God's word in regard to the New Covenant, we know what it reveals in regard to the two parties who meet in it. On God's side there is the promise to do for us and in us all that we need to serve and enjoy Him. He will rejoice in doing us good, with His whole heart. He will be our God, doing for us all that a God can do, giving Himself as God to be wholly ours. And on our side there is the prospect held out of our being able, in the power of what He engages to do, to "turn to Him with our whole heart," "to love Him with all our heart and all our strength." The first and great commandment, the only possible terms on which God can fully reveal Himself, or give Himself to His creature to enjoy, is," Thou shalt love the Lord thy God with all thy heart." That law is unchangeable. The New Covenant comes and brings us the grace to obey, by lifting us into the love of God as the air we breathe, and enabling us, in the faith of that grace, to rise and be of good courage, and with our whole heart to yield ourselves to the God of the Covenant, and the life in His service.

So Murray makes it clear

The New Covenant provides a guarantee, not only for God's faithfulness, but for man's too!

Now are you going to take God at his word? You can NOW simply believe that, what God has promised YOU - HE WILL PREFORM IT. Now you CAN place all your confidence in Him knowing and expecting that He will keep you.

More from Andrew Murray

Then there is the assurance of the sufficiency of Christ's finished redemption. All that was needed to put away sin, to free us entirely and for ever from its power, has been accomplished by Christ. His blood and death, His resurrection and ascension, have taken us out of the power of the world and transplanted us into a new life in the power of the heavenly world. All this is Divine reality; Christ is Surety that the Divine righteousness, and the Divine acceptance, that all sufficient Divine grace and strength, are ever ours. He is Surety that all these can and will be communicated to us in unbroken continuance.

It is even so with the assurance of what is needed on our part to enter into this life in the New Covenant. We shrink back, either from the surrender of all, because we know not whether we have the power to let it go, or from the faith for all, because we fear ours will never be so strong or so bold as to take all that is offered us in this wonderful Covenant. Jesus is Surety of a better Covenant. The better consists just in this very thing, that it undertakes to provide the children of the Covenant with the very dispositions they need, to accept and enjoy it. We have seen how the heart is just the central object of the Covenant promise. A heart circumcised to love God with all the heart, a heart into which God's law and fear have been put, so that it will not depart from Him---it is of all this Jesus is the Surety under the oath of God. Let us say it once more: Surely the one thing God asks of us, and has given the Covenant and its Surety to secure---the confident trust that all will be done in us that is needed--- is what we dare not withhold.

I think some of us are beginning to see what has been our great mistake. We have thought and spoken great things of what Christ did on the Cross, and does on the Throne, as Covenant Surety. And we have stopped there. But we have not expected Him to do great things in our hearts. And yet it is there, in our heart, that the consummation takes place of the work on the Cross and the Throne; in the-heart the New Covenant has its full triumph; the Surety is to be known not by what the mind can think of Him in heaven, but by what he does to make Himself known in the heart. There is the place where His love triumphs and is enthroned. Let us with the heart believe and receive Him as the Covenant Surety. Let us, with every desire we entertain in connection with it, with every duty it calls us to, with every promise it holds out, look to Jesus, under God's oath the Surety of the Covenant. Let us believe that by the Holy Spirit the heart is His home and His throne. Let us, if we have not done it yet, in a definite act of faith, throw ourselves utterly on Him, for the whole of the New Covenant life and walk. No surety was ever so faithful to his undertaking as Jesus will be to His on our behalf, in our hearts.

And now, notwithstanding the strong confidence and consolation the oath of God and the Surety of the Covenant gives, there are some still looking wistfully at this blessed life, and yet afraid to trust themselves to this wondrous grace. They have a conception of faith as something great and mighty, and they know and feel that theirs is not such. And so their feebleness remains an insuperable barrier to their inheriting the promise. Let me try and say once again: Brother, the act of faith, by which you accept and enter this life in the New Covenant, is not commonly an act of power, but often of weakness and fear and much trembling. And even in the midst of all this feebleness, it is not an act in your strength, but in a secret and perhaps unfelt strength, which Jesus the Surety of the Covenant gives you. God has made Him Surety, with the very object of inspiring us with courage and confidence. He longs, He delights to bring you into the Covenant. Why not bow before Him, and say meekly: He does hear prayer; He brings into the Covenant; He enables a soul to believe; I may trust Him confidently. And just begin quietly to believe that there is an Almighty Lord, given by the Father, to do everything needed to make all Covenant grace wholly true in you. Bow low, and look up out of your low estate to your glorified Lord, and maintain your confidence that a soul, that in its nothingness trusts in Him, will receive more than it can ask or think.

Dear believer, come and be a believer. Believe that God is showing you how entirely the Lord Jesus wants to have you and your life for Himself; how entirely He is willing to take charge of you and work all in you; how entirely you may even now commit your trust, and your surrender, and your faithfulness to the Covenant, with all you are and are to be, to Him, your Blessed Surety. If thou believest, thou shalt see the glory of God. What Christ has undertaken, you may confidently count upon His performing.

In a sense, and measure, and power that passeth knowledge, Jesus Christ is Himself all that God can either ask or give, all that God wants to see in us. "He that believeth in me, out of him shall flow rivers of living water."