Jeremiah 31:33 - Ellicott's Commentary On The Whole Bible

This shall be the covenant... — The prophet felt that nothing less than this would meet the wants of the time, or, indeed, of any time. The experiment, so to speak, of a law requiring righteousness had been tried and had failed. There remained the hope — now, by the Divine word that came to him, turned into an assurance — of a Power imparting righteousness, writing the “law in the inward parts,” the centre of consciousness and will, in which God required truth (Psalms 2:6), in the heart as the region at once of thoughts and of affections. In 2 Corinthians 3:3-6 we have a manifest reference not only to the idea, but to the very words of Jeremiah’s prophecy.