How does Montresor persuade Fortunato to come to his house?

Montresor takes a long time to fashion an elaborate lie that will entice Fortunato into the catacombs beneath his palazzo, where he can murder him. In the first paragraph, Montresor says

At length I would be avenged; this was a point definitely, settled—but the very definitiveness with which it was resolved precluded the idea of risk.

He wants his plan to be foolproof. When he encounters Fortunato celebrating on the streets during the carnival season, Montresor tells him his finely honed falsehood.

I said to him—“My dear Fortunato, you are luckily met. How remarkably well you are looking to-day. But I have received a pipe of what passes for Amontillado, and I have my doubts.”

“How?” said he. “Amontillado, A pipe? Impossible! And in the middle of the carnival!”

“I have my doubts,” I replied; “and I was silly enough to pay the full Amontillado price without consulting you in the matter. You were not to be found, and I was fearful of losing a bargain.....As you are engaged, I am on my way to Luchesi. If any one has a critical turn it is he. He will tell me—”

A pipe contains 126 gallons. Neither of these men would want the equivalent of 500 quart bottles of Amontillado sherry for personal consumption. They are not even sherry drinkers. The word "bargain" is what captures Fortunato's interest. He knows Montresor only bought the wine for resale. Many first-time readers of the story assume Fortunato wants to taste the delicious wine and show off his connoisseurship. This is not at all true. He is interested in the "bargain." He is a rich man. He could buy up the whole cargo of big oak barrels of fine Spanish sherry and make a small fortune. The wine only improves with age, so he could take his time about bottling and selling it by the case, probably to those British and Austrian millionaires Montresor mentions in his introduction. 

Fortunato doesn't need to taste Montresor's wine at all. He could go to the harbor and find a newly arrived Spanish ship with ease. There would be a whole shipload of Amontillado to sample, and he could make the deal on board. But Montresor has foreseen that possibility. He inserts the name Luchesi so that, if Fortunato declined to come to his palazzo immediately, Montresor could continue on his way on the pretext of consulting another connoisseur, and possible buyer, about his Amontillado. Fortunato can't let that happen. He must accompany Montresor to his home to keep him from talking to Luchesi. Otherwise, Fortunato would be competing with Luchesi in buying up the imaginary cargo of imaginary wine.

It was essential for Montresor to get Fortunato to his palazzo right away. Otherwise, if there was any delay at all, Fortunato could find out there was no Spanish ship, no Amontillado. Montresor would not only lose the chance to kill Fortunato, but he would arouse his suspicions. That would make it infinitely harder to entrap him at some time in the future. Montresor does not actually say that he has bought a pipe of Amontillado from a Spanish ship. He says:

"But I have received a pipe of what passes for Amontillado, and I have my doubts.”

The cunning Montresor has left himself a loophole. If necessary, he could make up some barely plausible lie, such as that he bought the pipe from a Venetian who had had it in his cellar for some time. But he doesn't have to do that. Fortunato imagines a Spanish ship full of big barrels of gourmet sherry which he can buy at a bargain price and sell at a great profit. He does not question Montresor any further because he does not want his gullible, trusting friend to suspect that he would be interested in buying any of the wine himself. He can go to Montresor's palazzo, taste the wine, make sure it is genuine, then get away and find this Spanish ship. No doubt he already plans to tell Montresor the wine is only ordinary sherry, just to eliminate him as a buyer. Montresor could only be so anxious to get an expert to sample his wine that night  if he intended to buy more while it was still being offered as a bargain. If it really is just ordinary sherry, Fortunato can forget about it. If it is genuine, he can buy up the whole cargo.

Montresor knows Fortunato thoroughly. He has had plenty of experience with this man. He knows what his shrewd, unscrupulous friendly enemy is thinking and planning. Fortunato has swallowed the whole cunning lie hook, line and sinker. He wants to rush to Montresor's palazzo as quickly as they can get there.

“Let us go, nevertheless. The cold is merely nothing. Amontillado! You have been imposed upon. And as for Luchesi, he cannot distinguish Sherry from Amontillado.”

Thus speaking, Fortunato possessed himself of my arm; and putting on a mask of black silk and drawing a roquelaire closely about my person, I suffered him to hurry me to my palazzo.