Aristotle lays out an almost mathematical proof in this chapter detailing why intellect is "the state concerned with first principles". First principles can not be an object of scientific knowledge because scientific knowledge is concerned with what is demonstrable and their are first principles to what is demonstrable. In other words, scientific knowledge does not look deep enough to touch first principles. Skill and Practical Wisdom are concerned with what is not demonstrable. So since everything demonstrable can be traced back to a first principle skill and wisdom obviously can't deal with first principles. Wise people "employ demonstration in certain cases" so first principles are not the concern of wisdom. This leaves only intellect.

". . . it is intellect that remains as the state concerned with first principles."