4:1-6 Christians who are well acquainted with the Scriptures, may, in humble dependence on Divine teaching, discern those who set forth doctrines according to the apostles, and those who contradict them. The sum of revealed religion is in the doctrine concerning Christ, his person and office. The false teachers spake of the world according to its maxims and tastes, so as not to offend carnal men. The world approved them, they made rapid progress, and had many followers such as themselves; the world will love its own, and its own will love it. The true doctrine as to the Saviour's person, as leading men from the world to God, is a mark of the spirit of truth in opposition to the spirit of error. The more pure and holy any doctrine is, the more likely to be of God; nor can we by any other rules try the spirits whether they are of God or not. And what wonder is it, that people of a worldly spirit should cleave to those who are like themselves, and suit their schemes and discourses to their corrupt taste?

6. We—true teachers of Christ: in contrast to them.

are of God—and therefore speak of God: in contrast to "speak they of the world," 1Jo 4:5.

knoweth God—as his Father, being a child "of God" (1Jo 2:13, 14).

heareth us—Compare Joh 18:37, "Every one that is of the truth, heareth My voice."

Hereby—(1Jo 4:2-6); by their confessing, or not confessing, Jesus; by the kind of reception given them respectively by those who know God, and by those who are of the world and not of God.

spirit of truth—the Spirit which comes from God and teaches truth.

spirit of error—the spirit which comes from Satan and seduces into error.