The Church must be one.

John 10:16 - there shall be one fold and one shepherd
John 17:17-23 - I pray that they may be one, as we are one
John 17:23 - that they may be brought to perfection as one
Romans 12:5 - we, though many, are one body in Christ
Romans 15:5 - God grant you to think in harmony with one another
Romans 16:17 - avoid those who create dissensions
1 Corinthians 1:10 - I urge you that there be no divisions among you
1 Corinthians 12:13 - in one spirit we were baptized into one body
Ephesians 4:4-6 -There is one Body, one Spirit, just as one hope is the goal of your calling by God. There is one Lord, one faith, one baptism, and one God and Father of all, over all, through all and within all.
Philippians 2:2 - be of same mind, united in heart, thinking one thing
Colossians 3:15 - the peace into which you were called in one body
St. Cyprian (c. 250AD) - "God is one and Christ in one, and one is His Church, and the faith is one, and His people welded together by the glue of concord into a solid unity of body. Unity cannot be rent asunder, nor can the one body of the Church, through the division of its structure, be divided into separate pieces." (On the Unity of the Church, 23)
Tertullian (c. 197AD) - "We are a society with a single religious feeling, a single unity of discipline, a single bond of hope," (Apology 39, 1)
St. Hilary (c. 4th century) - "In the Scriptures our people are shown to be made one, so that just as many grains collected into one and ground and mingled together, make one loaf, so in Christ, who is the heavenly bread, we know there is one holy, in which our whole company is joined and united" (Treatise 62, 13)
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