I was amazed when reading 2 Kings 21 how Manasseh had turned so badly from God's ways when he had the example of the destruction of Israel and the contrasting preservation and prosperity of his father Hezekiah. What was he doing? Could he not see the contrast between the way in which Hezekiah had prospered and been protected and the, now scattered, nation of Israel. Had other nations really prospered more than they for following all the ways of the gods he adopted? What made him move so dramatically back to the practices of Ahaz and the Israelite nation?
Well, we are not actually told directly. However, we can summise from his actions. Look at the range of gods he put up - it looks very like 'spread betting' ... lets get to worshiping as many gods as possible so that we are covered just in case one of them does not look upon us too well! This, I think, shows a basic insecurity - He wanted to be a prosperous and successful king, but with so many powerful nations around and with such a small country, how could he be? Instead of understanding that there was a great God in whom all trust could be put, he followed a natural inclination to protect himself with as much as possible.
In some ways he must have thought that this strategy paid off. He had a long reign with relative peace. Ahab, the earlier Israelite king, had a similar experience - great prosperity and international respect, yet a life following foreign gods. However, scripture records the true verdict on both men ... they did evil in the eyes of God!
The recent 'prosperity' movement had robbed us of a proper understanding of God's sovereignty and authority. Simple formulas do not work, because we cannot see all the variables or their values. Only He knows the beginning from the end. Only he can see the full extent of His purposes. He had a purpose of judgment for the wicked hearts of the people, who even in the reigns of Hezekiah and Josiah, those two Godly kings, only turned back to him on the outward appearance but not in the heart. The Kings rent their clothes, wept before the Lord and sought purity, but the hearts of the people still looked elsewhere, as we see from the rapid turn back to sin as soon as these Godly kings had gone.
The real question to ask ourselves, then, is this: Where is our true, total trust? Are we 'spread betting' in our lives, trusting on ourselves or the support of others, or the reputation we have built in our jobs, or the money we have in savings, or the love of our family, or whatever else, rather than in God? We may be seeing prosperity, but that does not mean our hearts are right. He longs for 'truth in the inward parts' (Ps 51v6), not the sham of worship when we are also trusting in other 'gods'.