Torah min ha-shamayim is the traditional claim that the Torah is God's revelation, given at Sinai, and it functions in Judaism as the ground of obligation rather than as a proposition to be assented to in isolation. If the commandments were given by God to this people, they bind; if they are the accumulated custom of an ancient nation, they may be admirable but they do not command.
Maimonides made it the eighth of his thirteen principles, and stated it strongly: the whole Torah now in our hands is the one given to Moses, and it is all from God. Traditional Judaism also holds that the written text was accompanied by an oral Torah, given at the same time and transmitted by memory before being written down as Mishnah and Talmud, which is what allows the written text to function as law at all. The written Torah says to do no work on the Sabbath and does not define work; the oral tradition supplies the thirty-nine categories.
The claim is not that the text is read woodenly. Rabbinic Judaism has always held that the Torah has multiple layers of meaning and that its interpretation is entrusted to the sages, with a famous Talmudic story in which a heavenly voice endorsing one rabbi's position is overruled on the ground that the Torah is not in heaven and the majority decides. Nor did traditional commentators avoid textual difficulties: medieval exegetes noticed the passages that appear to postdate Moses and discussed them.
What Orthodoxy and Haredi Judaism will not accept is that the Torah is a composite of documents by different hands from different centuries. That is the modern documentary hypothesis, and it is the point on which the movements of modern Judaism actually divide.