The Philistines for many years kept the Hebrew people in subjection; for they had lost the prerogative of faith, whereby their fathers had gained victories. Yet had not their Maker wholly blotted out the mark of their election nor the lot of their inheritance; but as they were often puffed up by success, He for the most part delivered them into the hand of their enemies, that thus, after the manner of men, they might be led to seek for themselves the remedy of their evils from heaven. For it is when any adversity oppresses us, that we submit ourselves to God; good fortune is wont to puff up the mind. This is proved by experience, as in other instances, so particularly in that change of fortune whereby success returned again from the Philistines to the Hebrews.
Source: Letter 19.9