Bennettt and Royle Chapter 10, “Figures and tropes”

In the chapter on “Figures and tropes,” Bennett and Royle describe metaphors as “the general term for the figure of resemblance, whereby one thing is likened to another.” In the following passage from Act 1, Scene 2 of William Shakespeare’s The Merchant of Venice, Nerissa says the following to Portia:

“Your father was ever virtuous, and holy men at their death have good inspirations, – therefore the lott’ry that he hath devised in these three chests of gold, silver, and lead, whereof who chooses his meaning chooses you…”

What do you think is the metaphorical meaning of lott’ry in this sentence? What are the implications of it for Portia and why must she follow its instructions?