Hamlet:
Not a whit, we defy augury. There is special providence in
the fall of a sparrow. If it be now, 'tis not to come; if it be not to
come, it will be now; if it be not now, yet it will come—the
readiness is all. Since no man, of aught he leaves, knows what is't
to leave betimes, let be. (Hamlet V.ii.191-194)

Hamlet has received Laertes' challenge by way of the King's toady, Osric. Horatio remarks that Laertes is known for his prowess with the sword and offers to make an excuse so that Hamlet can get out of the match. Both Hamlet and Horatio probably suspect that some foul play is afoot. But Hamlet refuses to put off the match. The above quote (on page 892 of our text) is his reply to Horatio.

What do you think Hamlet means? Note that the line about the sparrow is a reference to Matthew Chapter 10.