(g soft) means having the manners of genteel persons —i.e. persons of family, called gens in Latin.
“We must be gentle, now we are gentlemen.” - Shakespeare: Winter's Tale, v. 2.
The gentle craft. The gentleman's trade, so called from the romance of Prince Crispin, who is said to have made shoes. It is rather remarkable that the “gentle craft” should be closely connected with our snob (q.v.).
“Here Hans Sachs, the cobbler poet, laureate of the gentle craft, Wisest of the Twelve Wise Masters, in huge folios sang and laughed.” Longfellow: Nuremberg, stanza 19.
The gentle craft. Angling. The pun is on gentle, a maggot or grub used for baiting the hook in angling.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894