What is Church Unity?
Church unity has these aspects; Christians are united because they...
Some Christian groups insist that their denomination or Church is the one true Church and that non-members are outside the Church (and are probably not really saved). The Catholic Church claims to be the one true Church but allows that Protestants are actually Catholic — they just don't realize it! Many denominations and non-denominational denominations disparage what they call "religion" (not realizing that true Christianity is itself a religion).
Yet, putting all the pettiness, ignorance, and small-mindedness aside, every person who ends up redeemed is united with every other. So why are we so ill-mannered, boorish, and rude to our fellow Christians? It is because we need to study the Church.
The New Testament does not teach that Christian unity is based on institutional unity.
(Ephesians 4:3) Endeavouring to keep the unity of the Spirit in the bond of peace.
(Ephesians 4:13) Till we all come in the unity of the faith, and of the knowledge of the Son of God, unto a perfect man, unto the measure of the stature of the fulness of Christ.
In the context, Paul is clearly not referring to an institutional unity but to unity of the faith, of belief, of a brotherhood of love.
(John 17:21) That they all may be one; as thou, Father, art in me, and I in thee, that they also may be one in us: that the world may believe that thou hast sent me.
The unity within the Trinity is not institutional but a unity of essence and purpose.
(Romans 14:4) Who art thou that judgest another man's servant? to his own master he standeth or falleth. Yea, he shall be holden up: for God is able to make him stand.
Paul allows for various views regarding whether or not a person will eat food sacrificed to idols. Thus, he does not demand a fixed rule for all Christians on non-essential issues.