God shows that obedience was required of them. That which God commanded was, Hearken diligently to the voice of the Lord thy God. The promise is very encouraging. Let God's will be your rule, and his favour shall be your happiness. God was displeased with disobedience. We understand the gospel as little as the Jews understood the law, if we think that even the sacrifice of Christ lessens our obligation to obey.
Hardened their neck. A figure expressing obstinacy (see on 2 Kings 17:14).
Worse than. The people of Jeremiah’s day sinned against greater light. They did not profit from the experiences of their forefathers. Furthermore the prophet’s countrymen had set up objects of idolatry within the very precincts of the Temple (see Jer. 7:30; cf.2 Kings 21:7).