Does a church need other churches? How a pastor answers that question will define his pastoral leadership. If his answer is, "no, there is no real need for other churches, simply an option of partnership when helpful" then his connections to other churches will wax and wane over the decades, influenced greatly by the present cost or benefit of each partnership.
I would answer that yes, churches need other churches, at least if they desire to prosper over the generations. Here are a few reasons why.
Churches need other churches because:
1. New testament churches existed in partnership with one another. Corinth and Thessalonica owed their existence to the sacrifice and obedience of Antioch. Jerusalem needed the financial provision of the Gentile churches. Galatia needed the reassuring direction of the Jerusalem counsel. Countless churches benefited from the support the Philippians sent to Paul.Chritians and churches are made to be dependant. To say we do not need partnership is to say we don't need what the New Testament churches needed.
2. Churches need the wisdom of the wider body of Christ. All children of the reformation will affirm Sola Sciptura, and the priesthood of all believers, but of course they did not discover those doctrines for themselves, but because they have been handed down, defended, and articulated by other churches. For a congregation to assume that its pastors, both in the present and future, are immune to all doctrinal seduction is extremely unwise and sooner or later will lead to the downfall of the church. For pastors to assume this of themselves is to be wise in their own eyes. In my own view this motivates toward a certain established structure of partnership since the pastor who is currently dabbling in doctrinal disintegration is unlikely to pursue, at that moment, the evaluation and critique of other leaders. Previously established structures provide speed bumps and guardrails when we are slumbering at the wheel.
3. Churches are called to serve other churches in mission. People born of the Spirit are called to give their lives away to others. As crucial as local service is, there can be a kind of mutual benefit to servanthood within a local church. But when a church serves another church, either in establishing a church plant or in contributing to their mission, love as joyful sacrifice is practiced and the mission of the universal Church is advanced. We grow more and accomplish more together than apart.
4. Churches need counsel and encouragement in local crisis. Faithful pastors will certainly prepare for local conflict by teaching about godly speech, forgiveness, suffering, patience, faith, and love, but no amount of teaching can eliminate the possibility of some seasons of strife or trial in the future. Wolves, after all, will rise up from among us. The culture will always denounce Biblical principles. The flesh wages war against the Spirit. Even the best of spiritual shepherds will feel weak and vulnerable in any of these moments. Churches in crisis need more than the generic comfort of acquaintances; they need friends who are not ashamed of them, who are willing to sacrifice time and resources to help. A word of encouragement, timely counsel, a public commendation, a financial gift, solidarity in the face of persecution: these are life lines to a church that otherwise would be left to flounder in storms alone.
Partnership with imperfect churches means imperfect partnership. Friendship toward imperfect friends means sacrifice. Just the place for a church like ours.
Does a church need other churches? Every true church will be sustained ultimately by the Lord, His Word, and His Spirit, but the Lord works through the partnership of faithful but imperfect churches to uphold his Church, to conquer the gates of hell, and to proclaim the gospel of grace.
The chapter break between Leviticus 9 and 10 is unfortunate; it can conceal an important contrast. 
