Grace Perfects Nature

God’s graces are wonderful and effective; they are like a farmer sowing seed in the soil, while the natural moral virtues are like the soil, and the supernatural virtues are like plants. If the soil is moist and rich, then many beautiful plants will grow. If the soil is poor and dry, then thirsty little plants will grow. If the soil is abysmal, then probably nothing will grow. Therefore, children should work on—and parents should help their children work on—the development of the natural moral virtues. If the soil of the person’s character is rich in natural moral virtues, then the seed will grow into a beautiful tall plant of supernatural virtue. Supernatural graces and supernatural virtues are what we need to attain our supernatural goal, which is a loving union with the most adorable Trinity in Heaven.
It is true that God can give extra-special graces and can even circumvent nature—He is the Author of nature. At very needful and special times throughout history, God has done this is a very special way. This special action of God is what we call a miracle. Yet God—it seems—much prefers to work with human nature rather than around it. Indeed, God has ordained that grace build upon nature and not circumvent (go around) it. Indeed, that is the ordinary way, which—in our computer age—we might call “the default mode.”
Given the weakness of fallen human nature and consequent difficulty in the development of the natural moral virtues, one could understandably feel compelled to ask, “Why, then, doesn’t God just do a miracle and make it easy for us to be good?” Here is one answer:

God prefers to act by providence rather than miracles because He loves the natures of all the things He created and wants to perfect them rather than bypass them. He is like a wise, unselfish king Who exalts and empowers His servants rather than distrusting them and micro-managing His kingdom.(1)

After all, how many people do you know that would actually enjoy being a robot? Human beings tend to revolt at the idea of always having no choice but to act a certain way because someone has programmed them to do so. Actually, free choice of the will is part of human nature as created by God. It is much more beautiful and noble to choose to love and honor your Father than to be forced or programmed to do so.

Footnote
1. Peter J. Kreeft, The Philosophy of Tolkien, page 54.