The objective of this paper is to analyze some dimensions of the general Hervadian principle that nature as essence is both the principle of action of the human be-ing and its own purpose. To this effect, the first part of the paper is intended to glean the main meanings of nature in the classical world, and how it joins the idea of finality in Aristotle; and then in medieval thought represented by Aquinas. The second part, from the affirmation that na-ture is a measure of order and proportion, briefly develops four aspects of the problem in the context of the work of the great jurist of the University of Navarra. These aspects are: (a) empirical nature and nature as ratio; (b) nature as a measure of order and conduct; (c) nature and universal order (immanence and transcendence, and (d) finality in the world to come (a new civilization)