1 John 4:2

2Hereby, or by this, know ye He lays down a special mark by which they might more easily distinguish between true and false prophets. Yet he only repeats here what we have met with before, that as Christ is the object at which faith aims, so he is the stone at which all heretics stumble. As long then as we abide in Christ, there is safety; but when we depart from him, faith is lost, and all truth is rendered void. (82)

But let us consider what this confession includes; for when the Apostle says that Christ came, we hence conclude that he was before with the Father; by which his eternal divinity is proved. By saying that he came in the flesh, he means that by putting on flesh, he became a real man, of the same nature with us, that he might become our brother, except that he was free from every sin and corruption. And lastly, by saying that he came, the cause of his coming must be noticed, for he was not sent by the Father for nothing. Hence on this depend the office and merits of Christ.

As, then, the ancient heretics departed from the faith, in one instance, by denying the divine, and in another by denying the human nature of Christ; so do the Papists at this day: though they confess Christ to be God and man, yet they by no means retain the confession which the Apostle requires, because they rob Christ of his own merit; for where freewill, merits of works, fictitious modes of worship, satisfactions, the advocacy of saints, are set up, how very little remains for Christ!

The Apostle then meant this, that since the knowledge of Christ includes the sum and substance of the doctrine respecting true religion, our eyes ought to be directed to and fixed on that, so that we may not be deceived. And doubtless Christ is the end of the law and the prophets; nor do we learn anything else from the gospel but his power and grace.

2. “By this know ye the teacher of God; every teacher who confesses Jesus Christ as having come in the flesh, is from God; and

3. every teacher who does not confess Jesus Christ as having come in the flesh, is not from God; and this is the teacher of Antichrist, (or, the Anti Christian teacher,) of whom ye have heard that he is coming, and he is now already in the world.” — Ed