Here’s his extremely helpful summary of twelve arguments for congregationalism (p. 122):

1. The final court of appeal in a matter of discipline, which is the highest authority in a church, is the church (Matt 18:17).
2. Jesus says that the church has authority to make this assessment and judgment because it possesses the keys (Matt 18:18).
3. Jesus promises that his authoritative presence abides with two or three witnesses to his reign and to one another gathered in his name (Matt 18:20). This locates authority in a gathering. But to say that this promise applies to a gathering smaller than a church would divide a local church against itself and make the basic unit of kingdom authority something smaller than a church, or create churches inside of churches.
4. There is no mention of bishops or elders in Matthew 16, 18 or 28, nor does the New Testament give a single example of elders or overseers unilaterally exercising the keys.
5. The apostles treat the gathered congregation as something of an equal partner when selecting and affirming the seven proto-deacons.
6. Paul invokes the language of gathering with the authority of Jesus to act in Jesus’ name from Matthew 18:20 when he charges not only the leaders of the Corinthian church but the whole congregation to “hand this man over to Satan” (1 Cor 5:4-5). The judgment, to be clear, does not occur behind closed session doors.
7. Paul explicitly tells the whole congregation that it is their responsibility to judge (1 Cor 5:12).
8. Paul tells the Galatian churches that they should act as a check even on his apostolic authority when he departs from the gospel (Gal 1:6-9).
9. Paul affirms that the decision of the “majority” was sufficient for removing a man from membership (2 Cor 2:6).
10. Churches can exist without elders (e.g. Acts 14:23; Titus 1:5).
11. Much of the New Testament is written to whole churches.
12. This explanation has the advantage of corresponding more closely with the Greek conception of an ekklesia, which involved an assembly of citizens who shared rule together and each had one vote, not an assembly of subjects.

As I say: interesting.