Those who have been redeemed by Jesus Christ will unite together, submit to his word and use their gifts to serve one another
Belgic Confession Article 28 - The Obligations of Church Members: We believe that
since this holy assembly and congregation is the gathering of those who are saved and there is no salvation apart from it, no one ought to withdraw from it, content to be by himself, regardless of his status or condition. But all people are obliged to join and unite with it, keeping the unity of the church by submitting to its instruction and discipline, by bending their necks under the yoke of Jesus Christ, and by serving to build up one another, according to the gifts God has given them as members of each other in the same body. And to preserve this unity more effectively, it is the duty of all believers, according to God’s Word, to separate themselves from those who do not belong to the church, in order to join this assembly wherever God has established it, even if civil authorities and royal decrees forbid and death and physical punishment result. And so, all who withdraw from the church or do not join it act contrary to God’s ordinance.