Kevin DeYoung offers several practical reasons why church membership matters. At least one of the comments called for biblical proof for the idea of church membership. I offer these biblical considerations. 

There is a widespread notion that a truly Spirit-led congregation would not keep anything so earthy as membership records. This is an unfounded and unbiblical assumption which does not square with biblical history and teaching.

In the Old Covenant, God is a bookkeeper. In Exodus 32:32 we see a very interesting phrase. In a prayer, Moses pleads with God not to blot him out of “the Book you have written.” The Lord replies to Moses that He will indeed blot anyone who sins out of His “Book.”46 David declares in Psalm 9.5 that the Lord has “blotted out” the name of his enemies forever.47 In Psalm 40:7 David is assured that his righteousness is written on God’s scroll.

Many of these same themes regarding the “Book of Life” are evident in the Revelation of the Apostle John. To the Church in Sardis the Lord Jesus writes that He will not “blot out his name from the Book of Life” who is faithful and obedient to the Lord. Revelation 13:8; 17:8; 20:12,15; also refer to the Book of Life. It would seem that we are to conceive of a divinely kept book in which are recorded the names of all believers of all ages. This is not to say that there is an actual book, though there may well be.

In Psalm 69:28 David prays for the utter destruction of enemies and for them to be blotted out of “the Book of Life” and not to be listed with the righteous. In this same Psalm vv.9,10 David turns from the “book” to speak twice of the Qahal (which is translated in the LXX with Ekklesia and Synagogue (cf. Deuteronomy 9:10,14 where these two ideas are also closely connected). There is a close connection in David’s mind between the Qahal and the “book.”

Because God is revealed as a book keeper His Covenant people were also (according to the commandments of God) also book keepers.

There is significant evidence that in the Old Covenant there were membership rolls with the names of all the Covenant families and the Covenant heads of households. Genesis 5:1ff. speaks of the “book of the generations.” Moses worked from existing books in compiling his (selective) genealogies. This idea of membership roll figured conspicuously in the life of the Qahal. Later after the exile when the beginnings of the Synagogue can be traced, there is archeological evidence that there were membership rolls there as well. It took at least twelve men in good standing in the community to form a synagogue.

God commanded Moses in Exodus 17:14 to write down the destruction of the Amelakites because without this record there would not be any. In turn (Deutronomy 25.19), God will “blot out” the Amelakites. In Exodus 24:7 we read of the “Book of the Covenant” which contained the laws by which God’s Covenant people were to live. God commanded Moses to take a census of the people and to make a record of them (Exodus 30:11). Psalm 87:6 speaks of a “register of the peoples” (NIV). Ezekiel 13:9 speaks of a “register of the house of Israel” (NASB). There was a written record of the descendents of Aaron (Nu 3:10). It would seem to be beyond controversy that God’s people kept written records during the Mosaic theocracy. The question remains then whether similar practices continued into the New Covenant era.

There is a great deal of unity and continuity between the Old Covenant conception of the Qahal and the New Covenant Ekklesia. Thus there is good reason to suspect that there is continuity in the practice of record keeping. Remember that in both the Old Covenant and the New Covenant, one had to join the visible assembly and take the sign of the Covenant.

The most obvious examples of this sort of record keeping are the genealogies of Matthew 1:1-17 and Luke 3:23-38. We know from Acts that the Apostles met first in the temple, and then later during missionary journeys, in the synagogue. The organization of the synagogue did play some roll in the beginning of the visible Church. We see in Luke 4:18ff. that there was a reading of the Scriptures and an exposition of the Scriptures in the Synagogue. This practice was continued in the early New Covenant Church.

Another piece of evidence which adds to the presumption of Church membership in the New Covenant Church is the mention in Acts 16:5 that the Church grew greatly in numbers. If the Church in the New Covenant largely equals the Qahal of the Old Covenant and if it grew in numbers then we can fairly say that these converts ‘joined’ the Church.

There is positive evidence of record keeping (membership lists) in the New Covenant Church. The problem in the daily distribution of bread in Acts 6:1 assumes some sort of record keeping of eligible widows. In 1 Timothy 5:9-16 Paul speaks explicitly about a list of names of Christian widows who were eligible for financial assistance from the Church. He even lays out the qualifications to be on the list. If the Church kept such lists for financial aid, can we reasonably assume that these widows were not on a membership roll? Moreover we cannot help but notice that again Paul’s instructions regarding widows presupposes some sort of organized visible body of Christ who administered this aid to its members.