Asa used his period of rest from war to root out idolatry from Judah, and to build fortified cities. He was wise enough to know that the time of rest was a blessing, but that rest is not a given. Danger lurks from enemies within and without. So, the freedom and energy during peaceful times should be spent preparing for and preventing times of trouble.
When war came, they were ready, but they were still outnumbered against the Ethiopians. Fortunately, since they had rid themselves of the other gods, Asa could declare that the LORD stood between the weak and the mighty. The LORD defended them.
LORD, give us wisdom to rid ourselves of wrong allegiances, and to build up our defenses, so that in the time of battle, we can be confident of your rescue.
2 Chronicles 14