" Who have foregone the good of intellect"

(Canto 3, line 18)

"The good of intellect" stands for the highest truth. The idea comes from Aristotle's "Ethics", as Dante himself explains in the Convivio: "...to contemplate the truth, which is our ultimate perfection, as the Philosopher says in the sixth book of the Ethics when he says that truth is the good of the intellect." Here the phrase should be inferred to stand for God, who represents this highest truth.