When Jethro got saved he joined the church. Or to put it another way: I find it very noteworthy (and borderline instructive) that when he began being loyal to the one true God, Jethro “brought a burnt offering and sacrifices to God; and Aaron came with all the elders to eat bread with him before God.” Honestly reading that text–and the rest of the Scriptures, lead me to the conviction that being a knower and lover of the one true God through Jesus Christ enevitably leads folk to a “HERE I AM! HOW DO I CONNECT AND SERVE?” relationship with a less-than-perfect flesh and blood gathering of people; i.e. A Local Church. Here is something from 9 Marks Ministries of Capitol Hill Baptist Church.

Membership
What is it?

According to the Bible, church membership is a commitment every Christian should make to attend, love, serve, and submit to a local church.
Where is it in the Bible?

Throughout Old Testament history, God made a clear distinction between his people and the world (see Lev. 13:46, Num. 5:3, Deut. 7:3).
Christ says that entering the kingdom of God means being bound to the church “on earth” (Matt. 16:16-19; 18:17-19). Where do we see the church on earth? The local church.
The New Testament explicitly refers to some people being inside the church and some people being outside (1 Cor. 5:12-13). This is much more than a casual association.
The church in Corinth consisted of a definite number of believers, such that Paul could speak of a punishment inflicted by the majority (2 Cor. 2:6).
Not only does the New Testament speak of the reality of church membership, but its dozens of “one anothers” are written to local churches, which fill out our understanding of what church membership should practically look like.

Why is it important?

Biblical church membership is important because the church presents God’s witness to himself in the world. It displays his glory. In the church’s membership, then, non-Christians should see in the lives of God’s changed people that God is holy and gracious and that his gospel is powerful for saving and transforming sinners.