The difference between the old covenant and the new covenant —John Owen

“Behold, the days are coming, declares the Lord, when I will make a new covenant with the house of Israel and the house of Judah, not like the covenant that I made with their fathers on the day when I took them by the hand to bring them out of the land of Egypt, my covenant that they broke, though I was their husband, declares the Lord. For this is the covenant that I will make with the house of Israel after those days, declares the Lord: I will put my law within them, and I will write it on their hearts. And I will be their God, and they shall be my people. And no longer shall each one teach his neighbor and each his brother, saying, ‘Know the Lord,’ for they shall all know me, from the least of them to the greatest, declares the Lord. For I will forgive their iniquity, and I will remember their sin no more.”
—Jeremiah 31:31-34 & Hebrews 8:9-12

“Wherein, first, the condition of the covenant is not said to be required, but it is absolutely promised: “I will put my fear in their hearts.” And this is the main difference between the old covenant of works and the new one of grace, that in that the Lord did only require the fulfilling of the condition prescribed, but in this be promises to effect it in them himself with whom the covenant is made. And without this spiritual efficacy, the truth is, the new covenant would be as weak and unprofitable, for the end of a covenant (the bringing, of us and binding of us to God), as the old. For in what consisted the weakness and unprofitableness of the old covenant, for which God in his mercy abolished it? Was it not in this, because, by reason of sin, we were no way able to fulfill the condition thereof, “Do this, and live?” Otherwise the connection is still true, that “he that doeth these things shall live.” And are we of ourselves any way more able to fulfill the condition of the new covenant? Is it not as easy for a man by his own strength to fulfill the whole law, as to repent and savingly believe the promise of the gospel? This, then, is one main difference of these two covenants, — that the Lord did in the old only require the condition; now, in the new, he will also effect it in all the federates, to whom this covenant is extended. And if the Lord should only exact the obedience required in the covenant of us, and not work and effect it also in us, the new covenant would be a show to increase our misery, and not a serious imparting and communicating of grace and mercy. If, then, this be the nature of the new testament, — as appears from the very words of it, and might abundantly be proved, — that the condition of the covenant should certainly, by free grace, be wrought and accomplished in all that are taken into covenant, then no more are in this covenant than in whom those conditions of it are effected.”

—John Owen, The Death of Death in the Death of Christ