Antonio "is a good man", "he is sufficient", but "he hath an argosy bound to Tripolis....". Is the difference between " to be" and "to have" of some relevance in Shakespeare's Merchant of Venice?
Being refers to the state of something. In this sense, Antonio's state is one which makes him a good and sufficient man. To have refers to the possession of something. In this sense, Antonio has a boat (argosy). So, yes, there is a difference between to be (a person's state) and the have (the act of possessing).
I really do not think that there is any relevance outside of the typical use of each of the words.
One should most certainly bear in mind that it is Shylock who answers Bassanio in Act I, scene 3. Consequently, "good" in "Antonio is a good man" does not mean good-natured or benevolent. As a matter-of-fact,"be good" is synonymous with "have goods". I was just wondering whether there may be other passages in the play in which the limits between "be" and "have" are blurred or other passages which show that Shakespeare's use of "be" and "have" in this play is particularly relevant. I suggest taking a closer look at the trial scene.