WHAT IS USEFUL VS. WHAT IS CONVENIENT 

What is just and virtuous is useful for godliness. Not everything is useful. "All things are lawful unto me; but not all things are useful." The men of the world usually consider "useful" only those things that cause gain in business in the pursuit of money. For most people, what is useful is what is profitable. 

But for the true Christian, what is useful is what you lose on earth "that we may gain Christ." So we hold that what is useful is that alone that leads to godliness. 

There are things useful for the body and things useful because they lead to holiness. "Bodily exercise profiteth a little but godliness is profitable unto all things. "

St. Ambrose: Duties of the Clergy,  Book II, Chapter 6

(03-24-03)