Behold, the days come, saith the LORD, that I will make a {h} new covenant with the house of Israel, and with the house of Judah:

(h) Though the covenant of redemption made to the fathers and this which was given later seemed varied, yet they are all one and grounded on Jesus Christ, save that this is called new, because of the manifestation of Christ and the abundant graces of the Holy Spirit given to his Church under the gospel.

Wesley's Notes

31:31 Behold - And not only with the Jews, but all those who should be ingrafted into that Olive. It is not called the new covenant, because it was as to the substance new, for it was made with Abraham, Gen 17:7, and with the Jews, Deut 26:17,18, but because it was revealed after a new manner, more fully and particularly, plainly and clearly. Nor was the ceremonial law any part of it, as it was to the Jews, a strict observance of that. It was likewise new in regard of the efficacy of the spirit attending it, in a much fuller and larger manner.

Jamieson-Fausset-Brown Bible Commentary

31. the days . new covenant with . Israel . Judah-The new covenant is made with literal Israel and Judah, not with the spiritual Israel, that is, believers, except secondarily, and as grafted on the stock of Israel (Ro 11:16-27). For the whole subject of the thirtieth and thirty-first chapters is the restoration of the Hebrews (Jer 30:4, 7, 10, 18; 31:7, 10, 11, 23, 24, 27, 36). With the "remnant according to the election of grace" in Israel, the new covenant has already taken effect. But with regard to the whole nation, its realization is reserved for the last days, to which Paul refers this prophecy in an abridged form (Ro 11:27).

Matthew Henry's Concise Commentary

31:27-34 The people of God shall become numerous and prosperous. In Heb 8:8,9, this place is quoted as the sum of the covenant of grace made with believers in Jesus Christ. Not, I will give them a new law; for Christ came not to destroy the law, but to fulfil it; but the law shall be written in their hearts by the finger of the Spirit, as formerly written in the tables of stone. The Lord will, by his grace, make his people willing people in the day of his power. All shall know the Lord; all shall be welcome to the knowledge of God, and shall have the means of that knowledge. There shall be an outpouring of the Holy Spirit, at the time the gospel is published. No man shall finally perish, but for his own sins; none, who is willing to accept of Christ's salvation.