2 Samuel 23:3 The God of Israel said, the Rock of Israel spake to me, He that ruleth over men must be just, ruling in the fear of God.

These are the last words of David, tucked into the beginning of this chapter. It is a short segment comprising vv. 1-7, and this verse is the principle thought of the segment. In that we again see the tremendous emphasis scripture places upon the fear of the LORD, and here, specifically its' irreplaceability in the character and conduct of those in seats of authority.
The Giver of this commandment is referred to in 2 ways, as the God of Israel and the Rock of Israel, There is a lot in this, as it appears to be covenant language and prophetic, and in the NT Corinthians the Rock is said to be the Lord Jesus, so we have the Godhead joined in this edict to men. David is repeating these words to those who follow him. It is worth noting.
There is a single thought here that is required, and that is that the one in authority has only one manner in which he may rule, and that is that he must be just, where the main thought in the word translated just is that the character, actions, and judgments of the ruler must be of righteousness. The only ruler acceptable to the LORD is one who rules righteously, and it this requirement which he will answer to the Judge in the day of Judgment. It is a good idea to publicly voice the idea that our rulers need to rule in righteousness. Wisdom and a concern for the nation are good qualities, but the need of the day are those who will rule righteously. When was the last time we heard a candidate touted for their righteousness? It is nothing we need to be ashamed of. If that is the requirement placed upon them, it is good that they know what is required of them, and what they will answer to and for. Every one will, for every thing that they do.
And the one thing, the one place they are to find the ability and means to do this is via a fear of the LORD. And in that way is the only possible way to rule righteously. It cannot be done via any other means or effort. How we need to pray, in living in that fear ourselves, that the LORD would grant this fear to our leaders, even as He gave it to Nebuchadnezzar, the least likely one to ever find and use it. LORD, help us, we pray.