Rashi: It is comparable to a human king who was angry with his son. The son went to his father's close friend, and asked him to intercede on his behalf.

Rashi and Seforno: It implies that the fire subsided in its place, because, had it moved to one of the sides, it would have burned whoever lay in its path (so that the people would realize that the fire was not a regular one, but was Heaven-sent - Seforno).