Do you have specific questions?
The gist of it is this; each local congregation in the United Methodist Church does not adopt it's own bylaws or set it's own doctrine. All United Methodist Congregations are bound by the denominations doctrine and law, found in "the Book of Discipline". That doesn't mean local churches have no local authority. Each local church has a variety of decision making bodies. This varies, for example, from some congregational polity's where varying levels of local autonomy allow independent local congregations to essentially decide their own doctrine. Some denominations will have some denominational requirements for that doctrine, others very little.
Additionally, in the UMC, Pastors are not hired by the local church as an employee, but are instead sent by the denomination (specifically, the local conference). Clergy are credentialed through the denomination as well.
The "basis" sort of comes in two parts. You asked for Biblical justification; it's really more a traditional one. The Christian Church has almost always been connectional in some way. In Paul's epistles, you can see Pastors and Deacons being sent TO the church. And from the very early days of Christianity, pre-dating the New Testament in fact, that's exactly how the church was organized. It is in fact, how the apostles organized the church. While it varied, largely clergy were sent to local bodies and those local bodies adhered to some semblance of a larger doctrine; such as creeds. The Bible doesn't tell us which hymns to sing or what color to paint the door of the church, either. Ultimately, many issues of local church polity that aren't issues of fundamental doctrine, come down to questions of tradition, context, and experience.
