The Heads of Agreement 1691
Of Churches and Church-Members
1) We acknowledge our Lord Jesus Christ to have one Catholic Church, or Kingdom, comprehending all that are united to him, whether in heaven or earth. And do conceive the whole multitude of visible believers, and their infant seed (commonly called the Catholic visible Church) to belong to Christ's spiritual kingdom in this world: but for the notion of a Catholic visible Church here, as it signifies its having been collected into any formed society, under any visible human head on earth, whether one person singly, or many collectively, we, with the rest of Protestants, unanimously disclaim it.
2) We agree that particular societies of visible saints, who under Christ their Head are statedly joined together, for ordinary communion, with one another in all the ordinances of Christ, are particular churches, and are to be owned by each other as instituted Churches of Christ, though differing in apprehensions and practice in some lesser things.
3) That none shall be admitted as members, in order to communion in all the special ordinances of the Gospel, but such persons as are knowing and sound in the fundamental doctrines of the Christian religion, without scandal in their lives; and, to a judgment regulated by the Word of God, are persons of visible godliness and honesty; credibly professing cordial subjection to Jesus Christ.
4) A competent number of such visible saints (as before described) do become subjects of stated communion in all the special ordinances of Christ, upon their mutual declared consent and agreement to walk together therein according to Gospel rule. In which declaration, different degrees of explicitness, shall no way hinder such churches from owning each other, as instituted churches.
(The above is an extract from The Reformation of the Church by Iain Murray).