According to John of the Cross, a 16th century Spanish mystic, pure faith in God is like a ray of darkness. John believed that when we decide to live by faith, darkness can descend at each step along the way, as our former emotional props are systematically taken away. These props had served us well as gods providing certainty and security. Now gone, the vacuum created by our surrender to faith can actually lead to existential doubt and fear as we no longer have the certainty rooted in a lifetime of reliance on our own security program. That old life is in sharp contrast to walking by faith, where we don't feel certain about anything.
However, if we are able to patiently and silently let God be God, eventually an invisible trust will emerge. Such trust is not based on our own intelligence, self medication, good deeds, or anything other than God's mercy. Over and over again, our spiritual journey repeats these encounters with faith's ray of darkness as we progress along this path to the unknown. Remember God's call to Abraham, "Leave your country, your relatives, and your father's family, and go to the land that I will show you." In Abraham's life, we see a man who walked with God into the unknown and experienced God's blessing, only to be inspired to take further steps into the darkness that required more faith.
God calls us out of our small self, out of our secure, ego-driven existence. But after that, we don't have a clue where God is leading us. As the apostle Paul writes to the 1st century church in Corinth, paraphrasing the prophet Isaiah, "No eye has seen, no ear has heard, and no mind has imagined what God has prepared for those who love him." The only way to experience that prepared place is to surrender to live by not knowing. Our need for certainty is merely a big boulder in the pathway of trust that can't be mapped out in advance.