Merkle states for reason that church membership is needed: (1) biblical accountability, (2) biblical discipline, (3) the biblical use of gifts, and (4) the advance of God’s kingdom.
The Lord gave to the Church the charge to make disciples:
18 And Jesus came and said to them, “All authority in heaven and on earth has been given to me. 19 Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, 20 teaching them to observe all that I have commanded you. And behold, I am with you always, to the end of the age.” Matthew 28:18–20 (ESV)
The process of disciple making requires teaching, training, encouragement, admonition, living together, love. True discipleship will require commitment from both parties; such commitment will entail accountability of both parties to that relationship.
In the second chapter of Those Who Must Give an Account Benjamin Merkle provides an excellent and detailed explanation of the biblical basis for church membership. Those who question whether church membership is indeed a biblical requirement should consider the evidence and argument presented in this chapter before making such a conclusion.
Perhaps the strongest argument in favor of church membership presented by Merkle concerns the accountability relationship between the church and those called to lead the church. (It is true that many men and women have use positions of leadership within churches have purported churches for ungodly end through godly means. However the fact that many have abused their responsibility does not mean that such responsibility is on biblical, anymore than a fireman who becomes an arson means that one should not contact the fire department when their house is in flames.”
Merkle’s argument is far more detail than I can recount here. However, I would like to note a few highlights. Explaining the need for accountability, Merkle, writes:
Thus, biblical accountability is difficult, if not impossible, if the sheep have not formally committed to follow their leaders and if the shepherds do not know who they are responsible to lead.
Church members are called to obey, submit, and receive admonishment from their leaders. They’re refusing to commit to a local church, needed accountability is lacking, and cheaper often wonder away from the fold (and sometimes away from the Good Shepherd). Without accountability Christians often dry up spiritually and bear little fruit.
As for leaders:
Church leaders are called to shepherd those who have been entrusted to them and are therefore under their watch care. Without some formal recognition and acknowledgment of those who were members, this process of shepherding becomes increasingly difficult…. A Christian’s relationship to the local church should not be like a dating relationship for both sides are constantly guessing how the other views their relationship. Many Christians today want to date the church, making no formal commitment. The biblical picture of a relationship with Christ is not dating and marriage. Therefore, it is appropriate that we have a formal commitment to Christ’s visible church.