The Merchant of Venice has the dispute over Antonio's "pound of flesh" and Portia's need to find a husband via a lottery system which drive the plot forward. Shylock is beginning to realise that there may be an opportunity to get some revenge on Antonio for his poor treatment of Shylock and his "tribe" over many years.
Shylock reminds Antonio that many times, even in the "Rialto" which is a meeting place or Exchange where Merchants meet and do business, that Antonio has "rated" or criticized Shylock for his "moneys and my usances;" in other words, for his profit and the charging of interest on loans. Shylock has, he maintains, allowed it and suffered the abuse patiently because Jews ("our tribe") have borne "suff'rance" as if it were a "badge." The Jews have been persecuted for centuries to the point that others think they can mistreat him because he is a Jew and they do not need any other reason.
There is the name-calling - "misbeliever, cut-throat dog" and there has even been occasions when Antonio has spat on Shylock's coat ("gabardine') and for no reason other than the fact that Shylock makes use of his own means - "that which is mine own." So Shylock now considers Bassanio's request and again reminds Antonio that he actually spat ("rheum") on his beard and even kicked -"foot"- him over his doorstep (threshold) as if he were a stray dog - "a stranger cur."
So, if it's money Antonio wants ("moneys your suit"), Shylock wonders what he is expected to say - Does a dog have money or a stray have three thousand ducats? Perhaps Antonio expects Shylock to bow down to him and whisper in a "bondman's key" a bondsman being a slave so in a humble tone. Should Shylock remind Antonio of all this abuse and for "these courtesies" - for this special treatment (being sarcastic) and simply lend him "much moneys?"