“For another reason are there four Gospels: because these are pillars of the world. As the world is divided into four parts, east, west, north, and south, it was right that there also be four pillars. And for another reason are there four Gospels: because these contain four elements: teachings, commandments, warnings, and promises. To those who believe the teachings and observe the commandments, God promises the good things that are to come. But those who do not believe the teachings and do not keep the commandments, He threatens with the punishments that are to come.”

(St Theophylact, ‘Commentary on Matthew’)