Every Christian should join a church because Scripture requires it. Granted, there is no direct command in Scripture that says, “Every Christian must join a local church,” but two factors in Scripture indicate that every Christian should be a member of a local church:
a) Jesus established the church to be a public, earthly institution that would mark out, affirm and oversee those who profess to believe in him (Mat 16:18-19; Mat 18:15-20). These passages in Matthew assume your deep connection to a local church family as if to not have a church family isn’t even conceivable.
b) Jesus established the church to publicly declare those who belong to him in order to give the world a display of the good news about himself (John 17:21-23; see also Eph 3:10)
Jesus wants the world to know who belongs to Him and who doesn’t. How is the world going to know who belongs to Jesus and who doesn’t? They are going to see which people publicly identify themselves with His people in the visible, public institution that Jesus established for this very purpose, the Church.
Some people claim to be part of the universal church even though they belong to no local church, forgetting that in so doing they reject Jesus’ plan for them and His church. Jesus intends for all His people to be marked out as a visible, public group, which means joining together in local churches.
Moreover, Scripture repeatedly commands Christians to submit to their leaders (Heb 13:17; 1 Thess 5:12-13). The only way to do that is by publicly committing to be members of their flock and saying in effect, “I commit myself to listening to your teaching, following your direction and submitting to your leadership.” The simple truth is that there is no way that you can obey the scriptural commands to submit to your leaders if you never actually submit to them by joining a local church.
(Source: Found this article on social media. Not sure who the original author is.)