The Mishnah interpreted the words "he shall write a copy of this law in a book" in to teach that when he went to war, he was to take it with him; on returning, he was to bring it back; when he sat in judgment, it was to be with him; and when he sat down to eat, it was to be before him, to fulfill the words of , "and it shall be with him and he shall read in it all the days of his life."