Failure to observe the Sabbath, thereby showing covenant unfaithfulness, will result in curse. The Lord will kindle a fire in its gates, and it shall devour the palaces of Jerusalem and shall not be quenched.
This description of the destruction of Jerusalem is very similar to how Amos describes the destruction of the nations surrounding Israel and Judah (Amos 1:4, Amos 1:7, Amos 1:10, Amos 1:12, Amos 1:14; Amos 2:2; Amos 2:5; refer to Amos 1:14 for kindle
). It is the description of a city under siege being destroyed by fire.1 Every aspect of the promised blessing mentioned will be destroyed: throne, temple and people.
27 But if you do not listen to me, to keep the Sabbath day holy, and not to bear a burden and enter by the gates of Jerusalem on the Sabbath day, then I will kindle a fire in its gates, and it shall devour the palaces of Jerusalem and shall not be quenched.’”