Whenever we are trying to establish the meaning of one particular quote, it is always vital to make sure that we understand clearly the context of that quote to help us make sense of the particular quote. It is very dangerous to pull one quote out of the play and then try to interpret it without making sure that we understand its context. In this scene, Romeo is trying to buy some poison from the Apothecary, however, the Apothecary is very concerned about this, because it is illegal to trade in such poisons, and he could be killed for it if caught. Romeo therefore has to try and persuade the Apothecary to let him purchase his poison, and does so by pointing out how poor the Apothecary is:
Art thou so bare and full of wretchedness
And fear'st to die? Famine is in thy cheeks,
Need and oppression starveth in thy eyes,
Contempt and beggary hangs upon thy back...
Romeo points out the dire poverty that the Apothecary faces and how in want the Apothecary is, therefore using that as an argument to make the Apothecary except his money for the poison. In response to this, the Apothecary gives in, saying that he consents or agrees to the sale only because he is so poor and not because he wants to sell the poison.