Realizing that God's blessing resulted from following God, Asa told the people, "The land is still ours because we have sought the LORD our God; we have sought Him, and He has given us rest on every side" (14:7). God had done exactly that, starting Asa's reign with ten years of peace. God repeatedly emphasized that the land was "undisturbed" (14:1,5,6). "There was no one at war with him during those years, because the LORD had given him rest" (14:6).
In spite of the prevailing peace, Asa built fortified cities with abundant defenses. Eventually, the time came when he needed his large army of 580,000 warriors. Ethiopia attacked with an imposing army of 1,000,000 men and 300 chariots. In this daunting challenge, Asa demonstrated his trust in the God he had always followed. When Asa came to the battle, his dependence was not in his valiant warriors, but in Almighty God. He called out, "LORD, there is no one besides You to help in the battle between the powerful and those who have no strength; so help us, O LORD our God, for we trust in You" (14:11).
God responded to Asa's trust with a resounding defeat of the Ethiopians. In response to Asa's prayer, God "routed the Ethiopians" who "fled." "So many Ethiopians fell that they could not recover." They were "shattered," and there was "very much plunder." Asa's army pursued them all the way to their southern border where they "destroyed all the cities." The "dread of the LORD" fell on the Ethiopians. Judah "despoiled all the cities" and took "much plunder"; they "struck down those who owned" livestock and "carried away large numbers" of animals (14:12-15).
After the dramatic victory, God confirmed His hand of blessing on Asa by sending a prophet with this message: "The LORD is with you when you are with Him. And if you seek Him, He will let you find Him; but if you forsake Him, He will forsake you" (15:2). The prophet recalled that God had historically responded to Israel's cries of dependence. The prophet concluded by urging, "Be strong and do not lose courage, for there is reward for your work" (15:7).
Asa "took courage" from this message (15:8) and actually increased his efforts for God. Previously he had removed the idols from the cities of Judah; now he removed "the abominable idols from all the land of Judah" as well as from "Benjamin and from the cities which he had captured in the hill country of Ephraim" (15:8). Additionally, he "restored the altar of the LORD" (15:8).
Asa then gathered his citizens and the God-seeking immigrants from Israel for a great sacrifice accompanied by intense dedication. Those who feared God "entered into [a] covenant to seek the LORD God of their fathers with all their heart and soul," and they declared that "whoever would not seek the LORD God of Israel should be put to death" (15:12-13). The people sealed this covenant with an oath and with great rejoicing. Asa removed his own mother from being queen because of her idol worship. Finally, Asa donated his own treasures for use in the temple. God blessed this heightened devotion by giving "rest on every side," with "no more war" for the next twenty-five years (15:15,19).
Sadly, when the next conflict came, Asa did not rely on God as he had previously. King Baasha of Israel was fortifying a border city, trying to prevent his citizens from defecting to Judah. Instead of calling out to God, Asa sought help by sending treasures from the temple and palace to the king of Aram. Asa asked the king of Aram to break his treaty with Baasha and fight against Baasha instead. The plan worked. When Aram began capturing Israel's cities, Baasha abandoned his confrontation with Judah and turned to fight Aram.
In this seemingly successful resolution, Asa seized abandoned materials to reinforce his own cities. Asa lost, however, the treasures he had surrendered, and that wasn't his only loss. God sent a prophet to rebuke Asa, revealing that if Asa had not allied with Aram, he would have had the opportunity to conquer him. The prophet reminded Asa of the much stronger threat in the past, when God had given great victory due to the trust placed solely in Him. The greatest loss was that of God's blessing. The prophet declared, "The eyes of the LORD move to and fro throughout the earth that He may strongly support those whose heart is completely His. You have acted foolishly in this. Indeed, from now on you will surely have wars" (16:9).
Asa's heart for God was never the same again. He relied on man in the conflict with Baasha, and he did the same a few years later when he became severely ill. In spite of his serious illness, Asa "did not seek the LORD, but the physicians" (16:12). Asa's saddest response was toward the prophet who rebuked him. "Asa was angry with the seer and put him in prison," just for delivering God's message. Asa also "oppressed some of the people at the same time" (16:10). Asa had lost his tender heart.
I believe the primary reason for this change was because Asa hated war and wanted to avoid it at all costs. He knew the peace he enjoyed early on was connected to his seeking of God and therefore placed importance on following God. Even in peaceful times, Asa strengthened the military and the defenses. After the victory over Ethiopia, Asa escalated his devotion in response to the prophet's message that peace was a reward for seeking God. Then after decades of peace, when he saw the hint of war, he immediately took steps to remove the threat - steps that did not involve actual fighting on his part. Perhaps most telling was Asa's response to the prophet's message; when told that his kingdom would now face wars due to his failure to seek God, Asa became so angry that he put the prophet in prison and took out his frustration on his own people.
War was Asa's sensitive spot. For most of his life, God's blessing prevented Asa from facing the thing he dreaded. When war eventually threatened again, God could have handled the new situation just as easily as He had in the past. In the conflict with Israel, in the later wars, and in his illness, it was not too late for Asa to call on God for help. Unfortunately, when God allowed a threat and then predicted additional wars, Asa forsook God, angry that he had to face what he most wanted to avoid.
Because of the contrast between his earlier and later years, Asa's life provides a poignant example of God's blessing being on those who seek Him. When Asa sought God, he experienced an incredible victory and a nearly unbelievable stretch of peace. When Asa failed to seek God, he faced losses beyond what could be measured militarily, in addition to entering a time of wars and physical illness. Early success, even prolonged success, does not guarantee life-long success. Asa fell by refusing to humbly submit when God's choice conflicted with his own desires.