"And indeed, it," meaning: the Quran, "is in the Mother of the Book with Us," meaning: with Us, "exalted," meaning: high, "full of wisdom," meaning: fortified (muhkam). And the "Mother of the Book" is: the Preserved Tablet (al-Lawh al-Mahfuz). The interpretation of the Mother of the Book is: the entirety of the Book and its origin.
Muhammad said: The meaning of "We have made it" is: We have made it clear. Others besides Yahya said the same.