John Calvin Commentary Matthew 24:23

"Then if any man shall say unto you, Lo, here is the Christ, or, Here; believe [it] not." — Matthew 24:23 (ASV)

If any one shall then say to you. He again repeats what He had said about impostors, and not without reason. For there was great danger from this temptation: that wretched people, while their circumstances were troubled and desperate, would be deceived by false pretenses, would seek illusions instead of Christ, and would embrace Satan's delusions as if they were help from God.

Just as the Jews, when they were so severely oppressed because they had despised redemption, needed, at least, severe measures to restrain them from treachery, Satan cunningly offered them new hopes that would draw them still further from God. And certainly, when we are left without guidance in adversity, nothing is more destructive than to be deceived under the guise of God’s name by falsehoods that not only close the door of repentance to us, but also increase the darkness of unbelief, and eventually overwhelm us with despair and drive us to madness.

Therefore, the repetition of this statement was far from unnecessary when the danger was so great, especially since Christ warns them that false prophets will come prepared with no ordinary tools of deception—with signs and wonders designed to confuse weak minds.

For since God attests to the presence of His power through miracles, and since they are therefore seals of true doctrine, we should not be surprised if impostors gain credibility through them. Through this kind of delusion, God avenges the ingratitude of people, so that those who rejected the truth may believe a lie, and those who shut their eyes to the light offered them may be plunged deeper and deeper into darkness. At the same time, He tests the constancy of His followers, which then shines with greater brightness when they do not yield to any kind of deceptions.

Again, since our Lord declares that antichrists and false prophets would be armed with miracles, there is no reason why Roman Catholics should speak so arrogantly on this basis, or why we should be terrified by their boasting. In support of their superstitions, they plead miracles—those very miracles that the Son of God predicted would corrupt the faith of many, and which, therefore, wise people ought not to hold in such high regard that they are considered sufficient by themselves to prove any particular doctrine.

If it is objected that such reasoning would overthrow and set aside the miracles by which both the Law and the Gospel were confirmed, I reply that the Spirit engraved an undoubted mark on them, which removed from believers all doubt and fear of being mistaken. For when God displayed His power to confirm His people, He did not act in such a confused way as not to show the true and infallible distinction. Besides, the way miracles seal doctrine is such that the doctrine itself also shines in conjunction with them, dispelling all the clouds by which Satan darkens the minds of the simple. In short, if we wish to guard against deceptions, let us keep the connection between miracles and doctrine unbroken.