Well, it would help if you got the quotation correct. It's from The Tempest, Act III Scene 3. In this scene, Prospero's brother Sebastian, Alonzo the King of Naples, the counsellor Gonzalo and others are wandering about when Prospero starts creating magical illusions. The stage direction says "Enter several strange shapes, bringing in a banquet; they dance about it with gentle actions of salutation and, inviting the King &c to eat, they depart."This must seem pretty strange to Sebastian et al, but there it is. Sebastian says that now he's seen this, he will believe anything, "Now I will believe that there are unicorns."Do you believe that there are unicorns? Sebastian didn't used to, but now he does. The words (if correctly quoted) are exactly the sort of thing any 21st century English speaker might say, and need no explanation.