Now it is from the eternal law, which is the Divine Reason, that human reason is the rule of the human will, from which the human derives its goodness.
 Thomas Aquinas, Summa Theologica (1274). copy citation

add
Author Thomas Aquinas
Source Summa Theologica
Topic goodness reason
Date 1274
Language English
Reference
Note Translated by Fathers of the English Dominican Province
Weblink http://www.gutenberg.org/cache/epub/17897/pg17897-images.html

Context

“Therefore, since malice is contrary to goodness, the goodness of the will depends on the eternal law.
I answer that, Wherever a number of causes are subordinate to one another, the effect depends more on the first than on the second cause: since the second cause acts only in virtue of the first. Now it is from the eternal law, which is the Divine Reason, that human reason is the rule of the human will, from which the human derives its goodness. Hence it is written (Ps. 4:6, 7) : "Many say: Who showeth us good things? The light of Thy countenance, O Lord, is signed upon us": as though to say: "The light of our reason is able to show us good things, and guide our will, in so far as it is the light (i.e. derived from) Thy countenance." It is therefore evident that the goodness of the human will depends on the eternal law much more than on human reason: and when human reason fails we must have recourse to the Eternal Reason.
source