“Habakuk came and based them all on one, ‘A righteous shall live by his faith’” (Makkot 24a).
We should interpret “based them all on one,” meaning that the whole Torah is interpreted on one matter, which is faith. Once he has the basis, the Torah for the sake of Torah begins. But before the Torah, it is for the sake of “one,” meaning that through the Torah he will come to the Mitzva [commandment] that is called “one.”
It follows that we should learn Torah and see how the Torah speaks only of matters of faith. And besides learning the revealed in the Torah, we should also learn it in the manner of intimation, which speaks of matters of faith.