If the phrase in the text were used by a moral person, with a sincere and predominant desire to do his duty, it must, I conceive, be used in one of two senses: either (1) half-ironically, in recognition of a customary standard of virtuous conduct which the speaker is not prepared expressly to dispute, but which he does not really adopt as valid---as when we say that it would be virtuous to read a new book, hear a sermon, pay a visit, etc.; or (2) it might be used loosely to mean that such and such conduct would be best if the speaker were differently constituted.

ME Book 3 Chapter 2 Section 1