From Standpoint:
One of the distinguishing marks of a gentleman was that he did things because he knew they were the right thing to do, not because they would bring him personal advantage. Captain Oates was a very gallant gentleman. The idea of a gentleman was a more inclusive one than it sounds to modern ears. One of its greatest advantages was that you could define it so as to include yourself. You could behave like a gentleman, without possessing any of the social attributes which a gentleman might have: there was no need to possess a coat of arms, or a country estate, or engage in field sports, or wear evening dress. At least since Chaucer's time, there had been a distinction between the social meaning of the word, and the moral. It was evident that well-born people, who ought to know how to behave like gentlemen, did not always do so, while others sometimes did.
Philip Mason, whose perceptive study, The English Gentleman, was published in 1982, argues that “the desire to be a gentleman” runs through and illuminates English history from the time of Chaucer until the early 20th century. He suggests that “for most of the 19th century and until the Second World War” the idea of the gentleman “provided the English with a second religion, one less demanding than Christianity. It influenced their politics. It influenced their system of education; it made them endow new public schools and raise the status of old grammar schools. It inspired the lesser landed gentry as well as the professional and middle classes to give their children an upbringing of which the object was to make them ladies and gentlemen, even if only a few of them also became scholars.” This was a subject that interested so great a man as Cardinal Newman. In The Idea of a University he said that a liberal education makes “not the Christian, not the Catholic, but the gentleman”, and went on: It is well to be a gentleman, it is well to have a cultivated intellect, a delicate taste, a candid, equitable dispassionate mind, a noble and courteous bearing in the conduct of life; these are the connatural qualities of a large knowledge; they are the objects of a University . . . but they are no guarantees for sanctity or even for conscientiousness; they may attach to the man of the world, the profligate, the heartless.
More here.