In line 29, the Creed transitions to a discussion of the two natures of Christ. Again, the Creed warns that rejecting the truth of Christ’s two natures—Christ is at once true God and true Man—will lead to damnation. It’s important to understand what the Creed is not saying here. It is not claiming that in order to be saved, one must first possess a perfect knowledge of the two natures of Christ. It is indicating that to willfully depart from this doctrine is apostasy.

Lesson from the Creed

But it is necessary for eternal salvation
that one also believe in the incarnation
of our Lord Jesus Christ faithfully.

Athanasian Creed, line 29

Exposition from Scripture

The Creed here is not simply creating heretics ex cathedra. Rather, this warning is in line with statements we find in the letters of John.

1 John 4:2-3

This is how you know the Spirit of God: Every spirit that confesses that Jesus Christ has come in the flesh is from God, but every spirit that does not confess Jesus is not from God. This is the spirit of the antichrist, which you have heard is coming; even now it is already in the world.

CSB

2 John 9

Many deceivers who do not confess Jesus Christ as coming in the flesh have gone out into the world. Such a person is a deceiver and an antichrist. Watch yourselves so that you do not lose what we have labored for but receive a full reward. Anyone who goes on ahead and does not remain in the teaching of Christ does not have God. The one who remains in this teaching has both the Father and the Son. If someone comes to you and does not bring this teaching, do not receive him into your house. Do not even wish him well. For the one who wishes him well shares in his wicked works.

EHV

Are the letters of John any less insistent than the Creed? Certainly not! Again, we see that it is not adding to Scripture, but upholding it.

John says that those who deny the truth of the Incarnation—that Jesus Christ has come in the flesh—are antichrist. Thus, we see that antichrist isn’t really talking about a particular person (as in “the Antichrist”); but those who by their false teachings undermine Christ by denying His true humanity. That is, they teach a doctrine contrary to Christ’s, and contrary to the Scriptures, about who Christ is. He is true God and true Man: and they will name him Immanuel, which is translated “God is with us” (Matthew‬ ‭1‬:‭23‬ ‭CSB‬‬). In the beginning was the Word, and the Word was with God, and the Word was God … The Word became flesh and dwelt among us (John‬ ‭1‬:‭1‬, ‭14‬ ‭CSB‬‬). For the entire fullness of God’s nature dwells bodily in Christ (Colossians‬ ‭2‬:‭9‬ ‭CSB‬‬).

We shall see in subsequent posts that refusing to believe in the incarnation of our Lord Jesus Christ faithfully must finally leave one with no hope of salvation. Because our salvation requires that Christ be true God and true Man.

John calls anyone who believes and preaches otherwise a deceiver and an antichrist who does not have God. Likewise, he commands believers neither to welcome such a person, and not to even wish him well. This is a matter of utmost seriousness and dire consequence. It is urgent, and the Athanasian Creed teaches us to treat it as an urgent and serious matter.