Let us picture to ourselves as vividly as we can the situation that would have been created in the early Church, when errorists like Arius, Nestorius, and Pelagius arose, if men like Athanasius, Cyril, and Augustine had not earnestly opposed them. As far back as in the fourth and fifth centuries the Church would have lost the primary article of the Christian faith; the foundation would have been removed from beneath it, and it would have had to collapse. That was, indeed, impossible in view of the eternal counsel of God concerning the Church; however, because of that very counsel, God had to raise up instruments such as those teachers were. True, while they lived, they were hated and persecuted as malicious disturbers of Christendom, but for more than a thousand years their names have been beacon-lights, as names of great witnesses to the saving truth, and in eternity they will shine as the brightness of the firmament and as the stars forever and ever. Dan. 12:3. Let no one, then, be deterred from giving his testimony in behalf of the truth by the charge that he has a false spirit. That charge emanates only from unbelief.
Again, suppose Luther, after learning the truth, had indeed borne testimony for it to his immediate associates, but had not entered into conflict with the Papacy because of the great abominations which it had introduced into the Church, what would have happened? Christianity would have to remain under the soultyranny of the Roman Antichrist, and we all should still be subjects of it.
There is no question, then, but that both, yes, both these efforts are necessary: to defend the truth and to oppose every doctrinal error.
Walther, C. F. W., Dau, W. H. T., & Eckhardt, E. (2000, c1929, c1986). The proper distinction between law and gospel : 39 evening lectures. Forward by Jaroslav Pelikan. Includes index. (electronic ed.) (350). Saint Louis: Concordia Publishing House.