The communities neighbouring Jerusalem responded to this healing
with (literally) burning anger, great rage. It is the sort of anger that terrifies those in its path. For reasons not explained in the text this development clearly made them feel insecure and threatened.
7 But when Sanballat and Tobiah and the Arabs and the Ammonites and the Ashdodites heard that the repairing of the walls of Jerusalem was going forward and that the breaches were beginning to be closed, they were very angry.