The temptation of the church is mission drift, namely, to drift away from the mission to make disciples (Matt. 28:18-20). The result is the great o-mission. The church “fulfills the great o-mission” as it turns inward, loses sight of its purpose, becomes accustomed to the status quo, and lives in disobedience to Jesus' command to make disciples of all nations. 
This omission comes as a result of inward self-concern rather than a concern for "the other," those who live outside of faith in Christ. The church focuses primarily on itself, its needs, and agendas. It exhibits an exclusive attitude, being spiritually smug, distancing itself from contact with people who are far from God. It consequently becomes ingrown, apathetic, stagnate, and cynical. It suffers from the ecclesial illness known as "koinonitus" (from the Greek word koinonia, meaning fellowship), an imbalance of too much Christian fellowship to the neglect of mission to others. This tendency toward exclusive friendships, activities, and church programs which are inward-focused is dangerous to the health of the church and a denial of its mission to the world.
The church's omission may not be an oversight but a lack of insight as to what God wants to do in the world. The church does not see the world as God sees it, from his divine perspective. Hence, there is no burden for sojourners who live outside the family of God. A local church may be cordial to those who darken its doors and join for worship but it does not actively reach out to others within its sphere of relationships, its extended oikos (household). With such a lack of insight, such Christians becomes "keepers of the aquarium" meeting solely for the sake of the redeemed rather than engaging equally in redemptive relationships, participating with Jesus in fishing for men, (Matt. 4:19).
The goal of the church in this case quickly shifts to maintenance of the status quo. Services are conducted, programs are maintained, and ministries are continued entirely for the benefit of believers-- “servicing the saints.” In the course of events, the church develops a fortress mentality, focused mainly upon those within its walls, rather than on those outside. Its purpose becomes preservation of the organization, its history, traditions, structure and facility. Any mission that occurs is done to perpetuate and maintain the institution, not to redeem individuals, the community, or the world.
The church's omission may be directly related to disobedience to the commands of Jesus. The church understands the need to make disciples but does not act upon it, thereby proving itself irresponsible and disobedient to the great commission, resulting in what John Howard Yoder calls apostasy. Rather than reaping as workers in the harvest, Christians are more like "field residents," solely living among the crops (and perhaps squandering resources on themselves) but not laboring in the harvest. It is the church's preoccupation with itself that leads to the lack of obedience and measly results, if there are any results at all.
This sad state of affairs is all too common in the post-Christendom church today. Pastors and church leaders remain comfortable shepherding the flock, and justify this omission by all the "good things" that make up a busy schedule. When this is the case among leadership, little evangelism can be expected among the people. Such a state of affairs results in "fulfilling the great o-mission."
Unless Christ-followers take the initiative to reach out to people, and engage in redemptive relationships, the church will continue to diminish in number and influence within our post-Christian context. To remain in a "holy huddle," sitting back, wishing and praying, but never moving out as “sent ones” to make disciples is disobedience to the mandates to “make disciples of all nations” (Matt. 28:19) and to “love neighbor as self,” (Matt. 22:39).
 Dallas Willard, The Great Omission: Reclaiming Jesus's Essential Teachings on Discipleship (New York: Harper One, 2014).
C. Peter Wagner, Your Church Can Be Healthy (Nashville, TN: Abingdon Press, 1979), 78.
Donald McGavran and George G. Hunter III, Church Growth Strategies That Work (Nashville: Abingdon Press, 1980), 27.
 John Howard Yoder, Theology of Mission: A Believers Church Perspective (Downers Grove: IVP Academic, 2014), 185-192.
Bill Hull, The
(Old Tappan, NJ: Fleming H. Revell Company, 1990), 46. Disciple-Making Church
C. John Miller, Outgrowing the Ingrown Church (Grand Rapids: Zondervan, 1986), 34-35.