John Calvin on 1 John 4:5

5 They are of the world It is no small consolation that they who dare to assail God in us, have only the world to aid and help them. And by the world the Apostle means that portion of which Satan is the prince. Another consolation is also added, when he says that the world embraces through the false prophets that which it acknowledges as its own. The clause, “therefore speak they of the world,” is hardly a true rendering, for ἐκ never means “of,” in the sense of “concerning.” Macknight renders it “from.” Grotius paraphrases the sentence thus, “They preach things agreeable to the dispositions of the world;” and Doddridge thus, “They speak as of the world, as taking their instructions from it.” But ἐκ, like ex in Latin, means sometimes “according to,” as in Matthew 12:37, “For by (or, according to) thy words thou shalt be justified.” See also verse 34, “but of (or, according to) the abundance,” etc. Then this sentence may be thus rendered, “Therefore speak they according to the world:” that is, according to the views and principles of the superstitious and ungodly men of the world. — Ed We see what great propensity to vanity and falsehood there is in men. Hence false doctrines easily penetrate and spread far and wide. The Apostle intimates that there is no reason why we should on this account be disturbed, for it is nothing new or unusual that the world, which is wholly fallacious, should readily hearken to what is false.