The holy apostle Paul prescribed this kind of rule for his disciple Timothy and others in 1 Tim. 4:8: Train yourself in godliness; for the exercise of the body is of little use, but godliness is good for everything; and it contains the promise for this and the future life. The first part is a seria ad pietatis studium exhortatio (a serious exhortation to strive for godliness), a sincere, faithful admonition that Bishop Timothy and all true Christians should train themselves in godliness. The second part is an exhortationis illius pondus ac ratio, a very important reason for Timothy and all Christians to be motivated to train themselves in godliness.
The first part consists of these words: Train yourself in godliness. In order that we properly understand this apostolic principle, we need to take note of two things: First, what is meant by godliness. Secondly, what it entails for one to train himself in godliness. (Schola Pietatus-Volume 1 by Johann Gerhard, Repristination Press, p. 9)