Mercer, M. (1841). On entering upon the practice of every duty, so soon as we are convinced of its moral obligation. In M. Mercer, Popular lectures on ethics, or Moral obligation: For the use of schools (pp. 145-149). : Unknown Publisher.
http://dx.doi.org/10.1037/11941-026
There is no subject of more vital importance to your happiness in life than that, to which I am now about to invite your most serious attention. The evil spirits in man are said to have perceived and acknowledged the divine character of the Lord Jesus. "What have we to do with thee, Jesus, thou Son of the most high God?" From which you see evidently that a perception of the truth, and an obedience to its commands, may be completely separated. Indeed, there are few persons in the world who do not know their duty much better than they practice it. I would, therefore, endeavor to make you sensible of the imperious necessity for entering upon the performance of every duty so soon as you admit its obligation. In the first place we have evidence in every thing in life, to prove that whatever we would do well, we should do often. (PsycINFO Database Record (c) 2016 APA, all rights reserved)