From the Word
1 I therefore, a prisoner for the Lord, beg you to lead a life worthy of the calling to which you have been called, 2 with all lowliness and meekness, with patience, forbearing one another in love, 3 eager to maintain the unity of the Spirit in the bond of peace. 4 There is one body and one Spirit, just as you were called to the one hope that belongs to your call, 5 one Lord, one faith, one baptism, 6 one God and Father of us all, who is above all and through all and in all.
Ephesians 4:1–6, RSV
Christians should feel bound to maintain the unity of the Spirit, since they are all members of one body and partakers of the same spiritual blessings. They have the same priceless treasures — one God and Father in heaven, one Lord and Saviour, one Word, baptism and faith; in short, one and the same salvation, a blessing common to all, whereof one has as much as another, and cannot obtain more.
The unity of the Church does not consist in similarity of outward form of government, likeness of law, tradition and ecclesiastical customs. The Church is called “one holy, Christian Church,” because it represents one plain, pure gospel doctrine, and an outward confession thereof, always and everywhere, regardless of dissimilarity of physical life, or outward ordinances, customs and ceremonies. But they are not members of the true Church of Christ who, instead of preserving unity of doctrine and oneness of Christian faith, cause divisions and offenses by human doctrines and self-appointed works for which they contend, imposing them upon all Christians as necessary.
One of the wickedest offenses possible to commit against the Church is the stirring up of doctrinal discord and division, a thing the devil encourages to the utmost. This sin usually arises in certain haughty, conceited, self-seeking leaders who desire peculiar distinction for themselves and strive for personal honor and glory. They will give honor to no one, even when they recognize the superiority of his gifts over their own. In their envy and vengefulness they seek occasion to create factions and to draw people to themselves. Many are deceived and immediately respond to the new doctrine presented in specious words by presumptuous leaders thirsting for fame. Many weak but well-meaning ones fall to doubting; many become reckless pleasure lovers, disregarding all religion and ignoring the Word of God. Even they who are called Christians come to have hard feelings against one another, their love grows cold and faith is extinguished. Christians, then, should be careful to give no occasion for division or discord. They must strive against them, submitting to all suffering and performing all demands to prevent, so far as possible, any disturbance of the unity of doctrine, of faith and of Spirit.
Luther, Martin, and John Sander. Devotional Readings from Luther’s Works for Every Day of the Year. Augustana Book Concern, 1915, pp. 375–76.