The Restoration Movement, which gave birth to today's Churches of Christ, was founded by Barton W. Stone and Thomas Campbell. Stone was earlier than Campbell by a few years, and worked in Illinois at a time when Illinois was the American frontier.Stone had been an ordained Presbyterian minister, but he was excommunicated when he began serving communion to non-Presbyterians. He had preached at the famous Cane Ridge Revival and seen men and women converted by gospel preaching -- even though many of the preachers weren't fellow Presbyterians. Even Methodist and Baptist preachers brought people to Jesus. Indeed, in his autobiography, Stone declared, while near his own death many decades later, that not a single convert from Cane Ridge had strayed from Jesus. Each conversion had been clearly genuine as shown by the fruit of the Spirit borne by each.His rejection by Presbyterian authorities led him to participate in the dissolution of the Springfield Presbytery, an organization of Presbyterian congregations that decided to be Christians only but not the only Christians. To explain their decision, they wrote the Last Will and Testament of the Springfield Presbytery -- the earliest document of the Restoration Movement.

THE PRESBYTERY OF SPRINGFIELD, sitting at Cane Ridge, in the county of Bourbon. Being, through a gracious providence, in more than ordinary bodily health, growing in strength and size daily; and in perfect soundness and composure of mind; but knowing that it is appointed for all delegated bodies once to die: and considering that the life of every such body is very uncertain, do make, and ordain this our last Will and Testament, in manner and following, viz: Imprimis. We will, that this body die, be dissolved, and sink into union with the body of Christ at large, for there is but one body, and one spirit, even as we are called in one hope of our calling.Item. We will, that our name of distinction, with its Reverend title, be forgotten, that there is but one Lord over God’s heritage and His name one.Item.  We will, that our power of making laws for the government of the church and executing them by delegated authority forever cease; that the people may have free course to the Bible, and adopt the law of the spirit of life in Christ Jesus.Item. We will, that candidates for the Gospel ministry henceforth study the Holy Scriptures with fervent prayer, and obtain license from God to preach the simple Gospel, with the Holy Ghost sent down from Heaven, without any mixture of Philosophy, vein deceit, traditions of men or rudiments of the world—and let none henceforth take this honor to himself but he that is called of God, as was Aaron.Item. We will, that the church of Christ resume her native right of internal government—try her candidates for the ministry as to the soundness of their faith, acquaintance with experimental religion, gravity, and aptness to teach; and admit no other proof of their authority but Christ speaking in them— We will, that the church of Christ look to the Lord of the harvest to send forth laborers into His harvest; and she resume her primitive right of trying those who say they are apostles and are not.Item.  We will, that each particular church, as a body, actuated by the same spirit, choose their own preacher, and support him with a free will offering without a written call or subscription, admit members, remove offenders; and never henceforth delegate her right of government to any man or set of men whatsoever.Item. We will, that people henceforth take the Bible as the only sure guide to Heaven; and as many as are offended with other books, which stand in competition with I, may cast them into the fire if they choose: for it is better to enter into Life having one Book, than having many to be cast into hellItem.   We will, that preachers and people, cultivate a spirit of mutual forbearance; pray more and dispute less; and while they behold the signs of the times, look up and confidently expect that redemption draweth nigh.Item.  We will, that our weak brethren, who may have been wishing to make the Presbytery of Springfield their king, and wot not what is now become of it. betake themselves to the Rock of Ages, and follow Jesus for the future.Item. We will, that the Synod of Kentucky, examine each member, who may be suspected of having departed from the Confession of Faith, and suspend every such suspected heretic immediately, in order that the oppressed may go free, and taste the sweets of Gospel liberty.Item. We will, that J –—, the author of two letters lately published in Lexington, be encouraged in his zeal to destroy partyism. We will, moreover, that our past conduct be examined into by all who have correct information; but let foreigners beware of speaking evil of things that they know not.Item. Finally, we will, that all our sister bodies read their Bibles carefully, that they may see their fate there determined, and prepare for death before it is too late,

(emphasis added)Paul A. Crow, Jr. explains Stone's approach to the unity of the Spirit. Stone compared "book union," "head union," "water union," and "fire union" --

Book union was based upon an authoritative creed, confession of faith or church discipline. Head union was based upon a common opinion, and Stone learned that this approach was characteristic of many who denounced creeds and made the Bible their creed. He warned that to make interpretations of the Bible a system of salvation is equally wrong. Water union was based upon baptism by immersion of believers; made the primary criteria of faith, said Stone, immersion can become sectarian. These three concepts of union Stone rejected in favor of the fourth: the union of fire or the Spirit. This is the perfect union achieved not by the agreement of human opinion but faith in our “Lord Jesus Christ, the Savior of sinners, and by a cheerful obedience to all his known commands.” The road to union is the road toward the Lordship of Christ.

The Anatomy of a Nineteenth Century United Church (Lexington: Lexington Theological Seminary, 1983, pp. 16-17).Stone wrote as to book union,

For these books [creeds and confessions] have, from their very introduction, been the unhappy cause of disunion—and as light and liberty progress will be banished from the Christian community. ...Each one believed his opinion of certain texts to be the very spirit and meaning of the texts—and that this opinion was absolutely necessary to salvation.

Sound familiar? The Churches of Christ have long declared that we have "No creed but the Bible," and yet we do have a habit of making our opinions be absolutely necessary to salvation. Until God perfects our intellects in the general resurrection, we're going to disagree. Our minds are just as fallen as our morality. We cannot possibly unite this way.As to head union, Stone recognizes the equal impossibility that we'll ever all agree as to our hermeneutics. That is, by intellectual effort, we cannot unite because we not only can't agree on the meaning of the texts (book union), we can't even agree on the principles by which we should interpret the texts (head or hermeneutical union).Regarding water union, Stone wrote,

Water union was defined to be a union founded on immersion into water. But fact proves that this union is easily dissolved, and that immersion will not keep those who are immersed, united.

The Churches of Christ have preached baptism by immersion from their founding. And yet even while we were most loudly insisting on water union, we only became more and more disunited. It just didn't work. The water could not hold us together. Indeed, in many respects, it drove us apart, because we sought unity based on an agreed understanding of how and why to be baptized, which soon morphed into an agreed understanding on how to conduct the worship service, and then on how to govern the church, and then what to name the church, and then how to spend church treasury funds, and then ... well, we've not found a place to stop.As a result, Stone insists on fire union --

How vain are all human attempts to unite a bundle of twigs together, so as to make them grow together and bear fruit! They must first be united with the living stock, and receive its sap and spirit, before they can ever be united with each other. So must we be first united with Christ, and receive his spirit, before we can ever be in spirit united with one another. The members of the body cannot live unless by union with the head—nor can the members of the church be united, unless first united with Christ, the living head. His spirit is the bond of union. Men have devised many plans to unite Christians—all are vain. There is but one effectual plan, which is, that all be united with Christ and walk in him.

That is, only the divine Spirit can unite God's people, and so the only mark of unity needed are the fruit of the Spirit found in Gal 5. It's the work of the Spirit in our hearts that changes us so that we can be united. We don't change ourselves. We don't study and negotiate ourselves into unity. Rather, we submit to unity. Unity is found is humility and submission, not in the excellence of our knowledge and the perfection of our wisdom. Quite the contrary.Stone also wrote,

We have been too long engaged with defending ourselves, rather than the truth as it is in Jesus. Let us trust our little selves with the Lord; and rest not, till by faith in the promised Spirit and by incessant prayer we receive and be filled with it, like they were of old in the ancient order of things.

(Stone quotations are as quoted by Gary Holloway, "Circle of Fire: Barton Stone and a Spiritual Model of Unity," Issue 3 Council on Christian Unity (Dec. 2004).)The "ancient order of things" to Stone was not about precisely performing punctilious points of practice in the assembly. It was reliance on prayer and being filled with the Spirit.