Three things here are considered unmeasurable - or unsearchable. First we cannot search out the measure of the heavens. Astonomers concur with this fact. No matter how powerful our telescope - the heavens are pretty much unsearchable. And even if we could begin to fathom just how vast our universe was - we could never actually search it out and exhaust the information we could gather on it. The second thing we cannot search out is the depths of the earth. We have theorized just what is underneath us - but considering we are still discovering fish that we had no idea ever existed - I think it is safe to say that we cannot fathom all there is to know about the depths of the earth. The third thing is different from these first two. We are told that neither can we search out all there is about the heart of a king.
This is true on several levels. First, kings and leaders have information that the local people do not have - and probably will never have. I think it would absolutely blow our minds to realize how much information about different things - important things - comes across the desk of our president or any other ruler in our world. They do not have the time to inform us of everything that goes into their decision making processes - neither do they need to. This is why we need to pray that God would surround our leaders with wise and understanding counselors. Much of the decision making that happens in Washington D. C. happens because of the advice of those around our president. Pray that he will have godly, discerning advisors. We see what just one Daniel did in the kingdom of Babylon - one Mordecai in the kindom of Ahasuerus - and one Ahithophel in the kingdom of Absalom. Whether for good or for bad, those who advise our leaders will greatly affect our nation.
The king's heart is also unsearchable because they will not ever share all their reasonings for their decisions. Their role is to make decisions and lead a nation. Quite often pundits and writers will try to tell us what has gone on insider the minds of our leaders - but they don't really know. All we can hope and pray for is that they will make godly decisions that will bless our nation.
Finally, the heart of a king is just like every other heart among mankind. The king's heart is fallen. He is sinful no matter who he is. Thus, just like anyone else, the heart of the king is desperately sick and beyond even his own understanding. What we need to pray for is that our rulers are Christians who derive their wisdom and leadership from seeking God and knowing His Word. The king, like any other human, is sinful - and has aspects of his life that grieve him and plague him. He has weaknesses. This is the reason we need to pray for those in power and authority. They need our prayers because they do have to lead us. Our hope is that the One who searches all hearts - will search theirs as well. Our hope is that our leaders will have godly advisors and godly reasoning behind all that they do. Then we will have a blessed nation - because a nation ultimately must have its blessings from God. Oh that we would have leaders who turn to Him for that blessing.