It has no denominational requirements for membership. Catholicism had its beginning in the 7th century. Protestantism had its beginning in the 16th century. New Testament Christians belonged simply to the undenominational church. We must have an unreserved commitment to the Bible as the sole, objective standard in religion.
Unity can exist only when there is allegiance to a single objective religious authority.
We must be committed to being nothing, calling ourselves nothing, obeying nothing, and saying nothing except that which is authorized by the Word of God. Surely, it is possible to occupy an undenominational position. It is our plea for all to abandon the things that divide those who profess to be Christians, and occupy, with us, this undenominational ground. If we preach ONLY the gospel, it will produce in our day the one, true New Testament church that it produced in the days of the apostles, when no denominations existed. So the world may surely know I am loved, and sent by Thee.