Jeremiah 31:33

but this shall be the covenant that I will make with the house of Israel, when in the realization of His mercy the justice of His judgments will freely be acknowledged, After those days, saith the Lord, in the Messianic era, I will put My Law, the glorious message of His eternal Gospel, in their inward parts and write it in their hearts, so that it would become the inmost possession of all believers, and will be their God, and they shall be My people. The Word of the Gospel, implanted into the hearts of men by faith, is the fundamental principle, the guiding and driving power in their lives, by and through which the relation of the believer to the God of his salvation is established and maintained. Cf 2 Corinthians 6:18; 1 Peter 2:9.