Montresor uses Fortunato's pride to entice him to go and try the Amontillado. Montresor notes Fortunato's weakness in the third paragraph:
He had a weak point--this Fortunato--although in other regards he was a man to be respected and even feared. He prided himself on his connoisseurship in wine.
Knowing this, Montresor intended to exact his revenge on Fortunato by exploiting that weakness. He first mentions that he has the Amontillado but has his doubts about it, encouraging Fortunato to brag about his connoisseurship. Montresor then adds that he's going to ask Luchesi to sample the Amontillado in order to give him a judgment on it. Montresor knows Fortunato will say that he is the more seasoned wine taster. Fortunato adds, "And as for Luchesi, he cannot distinguish Sherry from Amontillado."
As they go further in to the catacombs, Montresor continuously suggests that they go back to save Fortunato's health and nagging cough. Fortunato, in his pride, takes this as a dare, as if Montresor is daring him to continue on. Fortunato urges them to continue on; thus, Montresor makes Fortunato the captain of the journey that will lead to his end (Fortunato's).