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?

2. Hereby—"Herein."

know … the Spirit of God—whether he be, or not, in those teachers professing to be moved by Him.

Every spirit—that is, Every teacher claiming inspiration by the Holy Spirit.

confesseth—The truth is taken for granted as established. Man is required to confess it, that is, in his teaching to profess it openly.

Jesus Christ is come in the flesh—a twofold truth confessed, that Jesus is the Christ, and that He is come (the Greek perfect tense implies not a mere past historical fact, as the aorist would, but also the present continuance of the fact and its blessed effects) in the flesh ("clothed with flesh": not with a mere seeming humanity, as the Docetæ afterwards taught: He therefore was, previously, something far above flesh). His flesh implies His death for us, for only by assuming flesh could He die (for as God He could not), Heb 2:9, 10, 14, 16; and His death implies His LOVE for us (Joh 15:13). To deny the reality of His flesh is to deny His love, and so cast away the root which produces all true love on the believer's part (1Jo 4:9-11, 19). Rome, by the doctrine of the immaculate conception of the Virgin Mary, denies Christ's proper humanity.