Church in Excess and Defect
St. Augustine said that the Church is a whore, but she is our mother. In time, we all experience the inadequacies of the Church, and this is especially true for Protestants, because few people remain members of the same church for the duration of their lives. In the Christian Life (CD IV/4), Karl Barth says the Church fails us in two ways, the first form by exceeding its mission and doing what it is not commanded to do, and the second way it fails us is by being in defect, and not doing what it is commanded to do. All Churches fail to fulfill the mission of God, by being in excess and defect in various ways. Karl Barth's dichotomy of error is a simple and helpful explanation of how the Church may acknowledge it's sin, in order to repent and fulfill its commission (c.f. Matt 28:19-20).
There are two main forms in which the paradoxical ignorance of God appears in the church, or, more exactly, there are two false developments that are inwardly related and correspond outwardly even though they move in opposite directions. The one sinister motif in both is that the church neglects, abandons, and loses its nature and task as such, thus becoming unfaithful to itself and denying its being as the church. 
A Church in Excess or Defect remains a True Church
Criticism of the Church must always be for the betterment and maturation of the church by calling a church to fulfill its calling by shedding its excess and adding to where it is in defect, but this calling should never result to telling a church that it is not a church! The excesses and defects is apostasy of the Church, but the Church's excesses and defects do not make the Church apostate. The Church is always being called unto holiness, not condemned unto perdition.
When this happens, when the church is involved in apostasy, there arises ignorance of God, desecration of his name, and darkness where there should only be light. . . . Especially in the church the darkness can never be total, for the church differs from the world in that it may live by and in the knowledge of God in his self-declaration. Even in its fall it cannot cease entirely to be the church, which will remain forever (Augsburg Confession, VII). 
The Church is simultaneously Sinful and Saintly
Jürgen Moltmann once explained that if Christians are simultaneously sinners and saints, as Martin Luther said, then the Church is a congregation of sinners and saints. The point is that the Antichrist is at work at every church, yet the church remains to be the true church of Jesus Christ, never the less.
The inconceivable thing is that even in the church Antichrist is at work as well as Christ, that is at one and the same time both the true church and the false, that in the church too there is an ambivalent knowledge of God that constantly threatens to turn into ignorance of God. The half-light in which the church exists is dreadful when it is involved in denial of its Lord and in apostasy from him. 
The Church in Excess
The Church in Excess is a church's first form of apostasy according to Karl Barth, and this occurs when a Church exceeds the command of God given to it. In the following quotations, Barth explains the dangers of a Church that is in excess.
The one form of the denial and apostasy is the church in excess, the presumptuous church which exalts itself and puffs itself up.
At this point one is naturally inclined as a Protestant to think especially of the Roman church. There may be something in this. But one should keep in view that the Roman church is not just a church in excess, involved in apostasy only on this side. One should also keep in view that, even if in less striking and classical form, the church in excess, in apostasy on this side, may be very clearly seen in the non-Roman Christian world, not only on its right wing among the Eastern Orthodox, Anglicans, and Lutherans, but also on the left wing, even down to the Baptists, though only on the margins.
The church in excess is the church exceeding the limit within which alone it can be the church of Jesus Christ: the limit of the basic determination that the living one to whom it owes the origin and constitution of its life, who in relation to it—and to it specifically—is the freely acting and speaking Lord, that this one is its sovereign. The threat is that it will serve its own needs instead of him, that it will become its own means of life and glory. Insofar as the church here is primarily interested in itself, and in its Lord only for its own sake, one might call it, in relationship to him, the introverted church. 
The Church in Defect
The counterpart form of apostasy is the Church in Defect, when the church fails to live up to its commission and neglects what is called to do by its Lord Jesus Christ.
The other form of apostasy is the church in defect, the church which does not take itself seriously enough because it is only half sure of its cause, which takes up this cause only hesitantly and with reservations and compromises, which only in a timid and uncommitted way ventures to give itself to its task.
At this point Protestantism of every denomination has reason to think first of itself. It might well be, of course, that in this sphere there has been and is too much of the church in defect because the grapes that the church in excess really wants are too high up for it, because it has experienced too much weariness and too many disappointments on the various ways to Rome, which attract it also and on which it has often gone quite a stretch. However that may be, too great a sense of the church is not as a rule the evident fault of Protestantism, but a painfully small trust in authority and power of him who has called, gathered, and sent out the church as his community is its fault,—a pitiably feeble courage when it should be resolutely facing the world with the task that has been set for it. Yet the Romans would be well advised not to rejoice too soon or too loudly on this side, as though this opposite error did not in any way concern them. It could be that the lack of trust and courage which characterizes the church in defect is the most fertile soil for the development of the church in excess, that the overblown sense of the church in the latter is simply a complementary reaction to the lack of genuine trust and courage that is more hidden here but still present. There is sin, within the walls as well as outside them, although again only on the margin.
The church defect is the church that is unfaithful to its determination vis-a-vis the world, which has been given to it with its establishing and upholding as the church of Jesus Christ. It is unfaithful because it neglects and denies the second aspect, namely, that its Lord—he is its determination—is the living Lord: the Lord who by his resurrection from the dead is in his death superior to death, and therefore to the world as the world that is marked and ruled by death; the Lord who overcomes the world, since God reconciled it to himself in him, so that his people need fear no one and nothing in the world. 
In the Command of God, at the end of CD II/2, Karl Barth compares the ethical commands of the Word of God to a disc. The disc encompasses all that the Lord God has commanded us (c.f. Micah 6:8), and contains all God expects us to do here and now that is described within this disc of ethical commands. We are commanded to walk the perimeter of this disc, and it is sinful to exceed this disc's circumference (in excess) as well as to shrink from its circumference (in defect), and therefore we must circumnavigate the perimeter of this disc of ethical commands without straying from it or falling short of it. True worship is to collectively walk the circumference together, and to collectively repeat back what God has said along this perimeter without going in excess over it or in defect under it. And true worship is when we collectively repeat all of what God has said, nothing less and nothing more, back to God in praise. And this is how we may interpret the Bible verses such as Rev 22:18-20.
[^1] Barth, Karl. The Christian Life: Church Dogmatics IV, 4: Lecture Fragments. Grand Rapids, MI: Eerdmans Pub., 1981. 135. Print.
[^2] Ibid. 135
[^3] Ibid. 136
[^4] Ibid. 136
[^5] Ibid. 137-8
Related: church, Church In Defect, Church In Excess, Ecclesiology, Karl Barth, Martin Luther