Why Moses' Face Shone Only After the Second Tablets

"And it came to pass, when Moses came down." From here the Sages said: One who gives a gift to his fellow, and it is a thing that is destined to be revealed, need not inform him of it, for behold today or tomorrow it will become known to him, as it is said, "and Moses knew not that the skin of his face shone." And on what account did the skin of his face not shine with the first tablets? Because the first ones were the writing of God, as it is said, "written with the finger of God" (Exodus 31:18); but the second ones, Moses wrote them from the mouth of the Almighty. Therefore the skin of his face was made to shine. And so the wise man said, "the wisdom of a man makes his face shine" (Ecclesiastes 8:1).