The “finest aspect(s)” are, according to the two explanations in the Long Explanation (Toh 3808 UT23703-093-001-12528–UT23703-093-001-12534, see “knowledge of all aspects”), either (in the first explanation) emptiness, as the root of all the other aspects, or (in the second explanation) the aspects that are included in the collections of the wholesome and those destined for what is right.