We know because God has not hidden Himself but has revealed Himself generously in His creation and in Scripture. By seeking and studying what God has revealed, we can make God’s thoughts our thoughts. We have, Paul wrote, the mind of Christ. We can know His design for human beings and for marriage and family, the purpose of government, the rightful end and object of worship, the significance of art and music and the place of science, and especially what has gone wrong with our world and what He’s doing to set it right. The ultimate goal is not to know things about God or even about His mighty acts in history. It is to know Him, and as Jesus put it, to love Him, with all our heart, soul, and mind.
For my thoughts are not your thoughts, neither are your ways my ways, declares the LORD. For as the heavens are higher than the earth, so are my ways higher than your ways and my thoughts than your thoughts.
Christians often cite these verses as meaning that God’s thoughts and ways are so transcendent and inscrutable, we cannot know them. This is, we are told, a reason for comfort for the Christian, especially when circumstances around us are confusing and painful. Some even use these verses to defend a kind of Christian anti-intellectualism. After all, if God is unknowable, why study theology at all? When having a “childlike” faith is confused with a purely emotive faith, there’s no sense in stewarding our minds to the knowledge and worship of God. Unfortunately, this way of approaching God has further devolved into the idea that if God is unknowable, we can’t really know His moral will when it comes especially to certain behaviors and lifestyles.
Of course, it is true that God is omniscient, and we are not. He not only knows vastly more than we can imagine or comprehend, He is the source of all knowledge. Because there is so much He has not revealed, there is no sense in which humans could ever know God exhaustively. All of which is why my friend Greg Koukl often says that Christians should never read a Bible verse. What he means is that Christians should never read only one verse by itself.
In the context of the verses before and after, Isaiah 55:8-9 does not suggest that we cannot know God’s thoughts and ways. In fact, Isaiah is saying the exact opposite.