When the Word of God shines on the human understanding, it enlightens it in such a way that it understands and confesses the Word and knows the certainty of it. This was the inner experience of David, and he spoke of it in Psalm 118 (ie 119) "The entrance of thy words, O Lord, giveth light; it giveth understanding unto the simple, . . ." meaning, those who in themselves are nothing, resembling the child whom Jesus set in the midst of his disciples to teach them humility (Matt. 18) saying: "Except ye be converted and become as little children, ye shall not enter into the kingdom of heaven. This concurrent or prevenient clarity found outward representation at the birth of Christ when the glory of the Lord shone round about the shepherds, and then the angel began to speak with them (Luke 2), and the shepherds believed the words of the angel and found all things as he had said.
Ulrich Zwingli (Sermon on the clarity and certainty of God's Word)