Matthew Henry on 1 Kings 11:1-8

There is not a more melancholy and astonishing instance of human depravity in the sacred Scriptures, than that here recorded. Solomon became a public worshipper of abominable idols! Probably he by degrees gave way to pride and luxury, and thus lost his relish for true wisdom. Nothing forms in itself a security against the deceitfulness and depravity of the human heart. Nor will old age cure the heart of any evil propensity. If our sinful passions are not crucified and mortified by the grace of God, they never will die of themselves, but will last even when opportunities to gratify them are taken away. Let him that thinks he stands, take heed lest he fall. We see how weak we are of ourselves, without the grace of God; let us therefore live in constant dependence on that grace. Let us watch and be sober: ours is a dangerous warfare, and in an enemy's country, while our worst foes are the traitors in our own hearts. (1Ki 11:9-13)