1 Kings 6:11-13. God tells Solomon "Concerning this house which you are building [i.e., the Temple], if you will walk in my statutes and obey my ordinances and keep all my commandments and walk in them, then I will establish my word with you, which I spoke to David your father. And I will dwell among the children of Israel, and I will not forsake my people Israel."

We know that Solomon ends up not walking in God's statutes and Israel suffers accordingly, but I am struck by how important the kingship, or being a leader, is. Solomon is King, God's anointed, and God says here that if Solomon walks in God's ways then God will not abandon the entire people. So all the people will benefit from Solomon alone being faithful, even if they themselves are not (although I am sure they will suffer individually due to their sins), and the entire nation will suffer if Solomon goes bad (and they do, because he does)!

God puts or allows leaders in their positions for a reason. They are to be leaders, what they do, their outlook, their morality, all affect their nation - they lead the people towards good or towards evil. When a leader allows himself to be corrupted by the evils of the world, the rest of the people will have no problem in doing the same. They won't even realize, necessarily, that they are doing wrong, because they're leader is setting the example, and thatis very bad.