68Simon Peter answered him, “Lord, to whom shall we go? You have the words of eternal life, 69and we have believed, and have come to know, that you are the Holy One of God.”
Commenting on these verses, Martin Luther once preached:
This example illustrates that we must not rely on man. We must learn to adhere to the Word of God, whether this is spoken by a disciple or an apostle, a saint or an ordinary man. Christ commands the 
apostles to heed the Word and not to follow the prompting of the devil or listen to the doctrine of the fathers [when they err].
Luther’s Works, vol. 23, 191
The person is of no consequence; nor is the person’s name important, whether it be Peter or Paul. The person is acceptable so long as he teaches faithfully. Therefore let the Word of God be your guide, and assure yourself that this is presented correctly. If the preached does that, he is above suspicion. But if he does not follow that guideline, then may he be accursed, even if it were I myself or an angel from heaven. St. Paul says to the Galatians (1:8): “But even if we, or an angel from heaven, should preach to you a gospel contrary to that which we preached to you, let him be accursed.”
Luther’s Works, vol. 23, 191-192