Our Lord Jesus Christ proclaimed quite clearly in Matthew 18 [:7] that His beloved Church would always have to suffer sets and factions when He said, “For it is necessary that temptations come, but woe to the man by whom the temptation comes!” Also St. Paul says in 1 Corinthians 11[:19], “There must be factions or heresy in order that those who are genuine may be manifest.” And 2 Peter 2[:1], “There will be false teachers among you, just as there were also false prophets among them.” That is exactly how things have happened since the beginning of Christendom, even at the time of the apostles and ever since, and thus it will be until the end of the world. For Christ is a King and Lord, and therefore He must also do battle and make war. But He battles spiritually with the truth against the lies, and so the lies take up arms and refuse to submit. That is how the sects come about and such riot and clamor arise in Christendom.
Therefore, no one should wonder or be appalled when he sees sectarian spirits and heretics rise up among the Christians and bluster so abominably against the truth. If you are a Christian and believe Christ and His apostles, then you must also believe and expect this, for they say, “Factions and scandal must come.” You cannot consider these words of theirs as lies or as idle, frivolous talk, but rather as speaking of honorable, important, terrible things, as it is fitting for God’s Word to speak; and you must not think it strange when they come, but learn to expect it, so that you can say: “Very well, let whatever is coming come. I have long known that factions would have to come. If it were not these, it would have to be others; if these were to cease, others would start.” If you want to have the precious Gospel, then you must also have the gates of hell and the devil [Matt. 16:18], so that you do not possess that Gospel along with love or with peace, as Christ says, “My peace I give you, not as the world gives” [John 14:27].
And, in sum, the devil is a blustering, rattling, and rumbling spirit; he cannot refrain from blustering and rumbling. Up till now, under the pope, he has blustered and rattled about in houses, in churches, in the field, and in the forest and has opened a soul-market there. He has hawked his wares and sold them in exchange for human souls, and thereby has dragged the Mass and all Christian works into purgatory—indeed, even into hell—and has stuffed all the world’s goods into lazy and gluttonous stomachs, indeed, he has buried them in the toilets and latrines of the cloisters and foundations of clergy. But now that this soul-market of his has been suppressed, he is beginning to rattle and rumble anew through the sectarian spirits. So, just as no one fears the rattling ghosts in their houses anymore, neither should we any longer be dismayed by rattling among the sects. There must be such rattling and rumbling so long as the world stands!
But everything must turn out for our good [Rom. 8:28]—and not by producing only a single kind of benefit. First of all, through it we become practiced in handling and keeping God’s Word all the more carefully, and thus we become more and more certain of the truth. For if there were no such sects through which the devil awakened us, we would become too lazy and would sleep and snore ourselves to death. Further, both faith and the Word would become dull and rusty among us until everything were destroyed. But instead such sets are our whetting stone and burnisher that sharpen and hone our faith and doctrine, so that they shine bright and pure like a mirror; and [we] also become acquainted thereby with the devil and his intentions and become ready and skilled for battle against him. None of this would happen if the sects left us in peace.
Martin Luther, Luther’s Works, American Edition, ed. Christopher Boyd Brown. vol. 59, Prefaces I, (Saint Louis: CPH, 2011) 267.