Martin Luther, the driving personality of the Protestant Reformation, made several distinctions that we continue to follow today. One of these is the distinction between God hidden and God revealed. Luther's desire was to convey a specific truth with this distinction, namely, that if we are to know the Lord, the Lord must reveal Himself to us. But in revealing Himself, God does not reveal everything there is to know about Him. He keeps part of Himself hidden, whether because we could not comprehend what He keeps hidden or because He simply chooses to exercise His sovereign freedom and not tell us certain things.
Deuteronomy 29:29 provides the essential biblical teaching that underlies this distinction. In this passage, Moses tells the Israelites that there are some things that are secret and belong only to "the Lord our God." Certain realities are for our Creator—and only our Creator—to know. At the same time, God has condescended to mankind in order to reveal to us certain truths about His character and plan. These truths are for us to know forever.
This passage indicates that the Lord has two wills—one hidden and one revealed. God's hidden will (also known as His decretive will, will of decree, or absolute will) includes all that He has ordained. His will of decree establishes every event in history, every thought and intention of every person, everything that ever happens. This will extends even to the ordination of evil, for the Lord works out everything according to the counsel of His will (Eph. 1:11). Importantly, not everything that God ordains in His hidden will is in itself pleasing to Him. Considered in themselves, He hates the evils He ordains, but He ordains them in order to overcome evil and achieve a greater good that does please Him (Rom. 8:28).
God's revealed will is also known as His will of precept or preceptive will. This will tells us what the Lord finds pleasing. Chiefly, the revealed will of God is His moral law. When Scripture calls us to do the will of the Lord, it is this will that is in view. We cannot know His hidden will except in retrospect. We can look back in history and know what was part of the Lord's hidden, or decretive, will up until this point because God's decretive will always comes to pass. Whatever happens in history manifests what He ordained in His sovereign but hidden will. Yet we are not called to seek out this hidden will, which we cannot know in advance anyway because God hides it from us. Instead, we are to live by what the Lord has revealed in His preceptive will. As we obey His commandments, we please our Creator.
The distinction between God's hidden will and His revealed will gives us a great deal of freedom. We do not have to worry about His hidden will, because we cannot know it anyway. But as long as we seek to obey His revealed will, we may freely do whatever is in accordance with this will. If, for example, we are presented with two choices for work and both of them do not entail sin, we can choose whichever job we like better without worrying that we are displeasing the Lord.