God’s will is something we can know exists – but not something we can peer into (Unless God reveals… Deut 29:29).
Prayer is our communication with God and it must include our desires weather good or bad, right or wrong. God does not hope that we will pray according to His (secret) will, we always will! God allows us personal access to Him which works with His will to accomplish things in the world. Prayer is a means God employs.
Hezekiah and the power of prayer
In the case of Hezekiah, it was God’s decree (secret will) that Hezekiah would come to the point of death and have his life extended through prayer. It was not His will that Hezekiah would die and God’s mind was changed by the kings prayer. However, prayer was the means of life extension! Just like a surgery might prolong someones life – the surgery is the means God uses. Of course, God uses multiple means for many things. But prayer is one of the most significant means.
God’s will is not an impersonal force that must be accomplished no matter what. God’s will is His total sovereignty over all creation and all their actions working for His glory and the elects good. Since nothing is outside His will, that includes our thoughts, struggles, natures tendencies, fears etc. Everything is a means of His will. But not everything is equally important. God is drawing everything to unity in Himself with Christ and the church as the head of the universe (Eph 1)
Understanding the Privilege of Prayer
This makes prayer a means regarding power, and an ends regarding relationship. God’s will is to use our prayer to accomplish, but so much more than that, it is to enjoy us (and we to enjoy Him) through our prayer.
DON’T over think the power of prayer! Simply acknowledge that God is sovereign and you are not a robot. Focus instead on the privilege of prayer! You are the friend of God in prayer. He is your closest confidant. Look at the privilege God gave to Abraham in Gen 18 – to argue with Him about destroying Sodom for the sake of Lot – that’s awesome privilege!