Nature Vs. Grace - Francis Schaeffer

Nature, the lower: the created; earth and earthly things; the visible and what happens normally in the cause-and-effect universe; what man as man does on the earth; diversity, or individual things, the particulars, or the individual acts of man.

Grace, the higher: God the Creator, heaven and heavenly things; the unseen and its influence on the earth; Unity or universals or absolutes which give existence and morals meaning.

http://www.jasonyounglive.com/2010/02/27/nature-vs-grace-key-contrasts/

After some research I have found that the original concept of Nature vs. Grace comes from a 15th century book called the Imitation of Christ by Thomas Kempis. I am not Catholic, nor am I familiar with this work which embarrassingly is "perhaps the most widely read devotional work next to the Bible," according to Wikipedia (two sources are given). Francis Scaeffer is a 20th century Christian philosopher.