Unless the LORD builds the house, the builders labor in vain. Unless the LORD watches over the city, the guards stand watch in vain.
– Psalm 127:1b (NIV)
It seems to me a common thread in the Old Testament is the fate of cities. Often in ancient times, cities were incredibly important and defined whole people groups. Think Athens versus Sparta. The Bible makes clear time and again that the fate of cities is in the Lord’s hands.
If the Lord wants to take out a city, He will. See Sodom and Gomorrah. If the Lord decides not to take out a city, He won’t. See Nineveh in the Book of Jonah.
It also seems to me that God extends this concept all the way up to entire nations, and all the way down to single households.
For an excellent discussion on Sodom and Gomorrah and the events leading to their destruction, read this sermon by Keith Krell.