The body is to grow by exercising Christ's gifts so that it doesn't get blown around by the waves and winds of false doctrine. John Piper illustrates this as a challenge not to be jellyfish and leaves, but rather to be made into dolphins and trees... transformed together by Christ... transformed as we live together and speak the truth to one another.
The argument continues with more and more focus on the way God's people speak to one another. The essence of relationship is speech. We could speak lies to one another, arguing and fighting. Or we can speak truth and peace. Anger that leads to sin gives the devil a foothold in the church, which is a far cry from the unity of the Spirit.
We're called in our relationships not to oppose the Spirit, not to grieve him... What then? We should throw out bitterness, wrath, anger, clamour, slander and malice. These are the chief ways that the Spirit is grieved: broken relationship in the church.
Let no corrupting talk come out of your mouths, but only such as is good for building up, as fits the occasion, that it may give grace to those who hear. And do not grieve the Holy Spirit of God, by whom you were sealed for the day of redemption. Let all bitterness and wrath and anger and clamor and slander be put away from you, along with all malice. Be kind to one another, tenderhearted, forgiving one another, as God in Christ forgave you. -- Ephesians 4v29-32
The unity of the Spirit is not a vague concept, rather it is God's supernatural work of creating the unity of the church. People who would once have been alienated from one another now in unity. Not that relationship is not possible outside the church, but the unity God is creating is to be deeper and longer lasting....
The Spirit-filled church must commit to relationships and not tearing one another down. Speaking the truth of the gospel in our relationships... supporting one another. Likewise there can be no churchless Christianity... becoming a Christian brings us into relationship with God and Christians. And in those relationships we cannot say I love you but that doesn't mean I have to like you. True relationships require commitment, time and communication.
Grieving the Spirit happens in broken relationships. We're in disobedience to God and are paining the Holy Spirit. We must repent. And where possible seek reconciliation. The Spirit has created unity, let us live in that.... Pursing kindness, tenderheartedness, forgiveness... just as we are forgiven in Christ.
"Let us cry aloud to the Holy Spirit, who is certainly grieved with his church, and let us purge our churches of everything that is contrary to his Word and to sound doctrine, and then the Spirit will return, and his power shall be manifest" -- CH Spurgeon