Charles Ellicott Commentary Jeremiah 17:27

"But if ye will not hearken unto me to hallow the sabbath day, and not to bear a burden and enter in at the gates of Jerusalem on the sabbath day; then will I kindle a fire in the gates thereof, and it shall devour the palaces of Jerusalem, and it shall not be quenched." — Jeremiah 17:27 (ASV)

Then will I kindle a fire ... —The fire is figurative rather than literal: the “fierce anger” of the Lord which man cannot quench, and which brings destruction in its wake, of which an actual conflagration may have been the instrument (Hosea 8:14; Amos 1:14). Compare Jeremiah 7:20; Jeremiah 21:14.