Knowledge without action does not benefit anyone. The Pharisees and Teachers of the Law did not let their eyes to see nor their ears hear, they were blinded by their own righteousness. the Gospel of Luke is calling us, to may have certainty concerning the things you have been taught. Levi, may have heard the Jesus, and even being baptized before, but when Jesus "saw" (gave him worth in His eyes) him, he could not do anything else but to surrender to Him by His love.