It's easy to talk about "unity within the church" as long as we're talking in the abstract. However, what do you do when a Christian brother or sister offends you or sins against you? Do you "write them off" and go your separate ways? I submit this is often the easier choice, but Jesus and the standards of his kingdom rule do not permit us to do so.
Let's consider the significance of Jesus's prayer to the Father in John 17 when he prays:
The goal is for all of them to become one heart and mind-Just as you, Father, are in me and I in you, So they might be one heart and mind with us. Then the world might believe that you, in fact, sent me. (John 17: 20–21, The Message)
Upon reading these words, we must recognize that any break in relationship threatens to undermine the essential witness of the church and its message. Notice Jesus says When we are of one heart and mind the world might believe that Yahweh [the God of Israel] is the one true God and Jesus, his son, is the promised King come to reign over and bring restoration to his world through his people: the church!
Some suggest Jesus is only referring to a nebulous spiritual unity; however, Jesus emphasizes a form of unity that is visible to the watching world, and thus must be referring to a relational unity that can be observed. This does not mean we have to agree on every point of doctrine-we don't! Nor does it mean we are to embrace some sort of fuzzy ecumenism in which we compromise the truth of the gospel or overlook sin within the church.
Jesus continues by saying, "Father, I want those you gave me To be with me, right where I am, ... I have made your very being known to them-Who you are and what you do-And continue to make it known, so that your love for me Might be in them exactly as I am in them" (v. 24, 26, The Message, emphasis mine). In saying this, Jesus establishes the love of the Father (the "very being" of God) for the Son as the standard by which we are to love others.
This love is not like the world's, which is conditioned upon the response or attitude of the recipient-it is a never-ceasing love that is outrageous in its generosity! It is a love that always protects, always trusts, always hopes, always perseveres (see 1 Cor. 13).
Thus when we find ourselves at odds (no matter how justified) with our brother or sister, our only response is to run to them with an attitude of reconciliation. We are compelled by the love of God to do so for fear that if we don't, we are reinforcing doubt about the truth of God and salvation in Christ.
Furthermore, we are to pursue reconciliation with others in a spirit of forgiveness in the same way the Father pursues reconciliation with us! In this relationship we are the offending party-utterly in the wrong-and yet God graciously seeks after and forgives us "while we were still sinners." It is utterly one-sided, an act of outrageous generosity from the Father! This is the way of the kingdom in which God's power is manifested and true and mutual reconciliation can follow.