When referring to Aristotle, why are first principles important?

Aristotle seems to think that each first principle has both a logical and an explanatory role in a treatise. Yet it is typical, especially in treatises which are introductory to a topic, to have principles which serve a logical and explanatory role, but also to have principles whose only explicit role is pedagogical. For they serve no obvious role in the demonstrations. Such might be the definitions of point and line in Elements i. Hence, if there is a relation between Aristotle's conception of first principles and those of the mathematicians, Aristotle provides an ideal framework based on contemporary mathematical practice and which may or may not have been noticed by authors such as Euclid.