Because narrow is the gate, and narrow is the way, which leads unto life, and few there be that find it.
All Commentaries on Matthew 7:14 Go To Matthew 7
Jerome
AD 420
Attend to the words, for they have an especial force, “many walk” in the broadway - “few find” the narrow way. For the broad way needs no search, and is not found, but presents itself readily; it is the way of all who go astray. Whereas the narrow way neither do all find, nor when they have found, do they straightway walk therein. Many, after they have found the way of truth, caught by the pleasures of the world, desert midway.