As we have mentioned earlier, we are saved into the community of believers, the Church, through baptism. Once foreigners to God and to God's people, we are now brought into communion with God and with the people of God.
This community of believers, the Church, certainly consists of all believers everywhere. It is therefore true that whoever believes the Gospel is already part of the church. However, this universal Church is expressed in physical assemblies of believers for the purpose of worshiping God and hearing the proclamation of God's Word.
Faith in Christ is expressed in joy, gratitude and desire to please God. Likewise, being now in communion with God and with God's people will be expressed in the desire to physically be a member in a local Church. Therefore, anyone who believes in God will naturally desire to join his new brothers and sisters to worship God, to hear His Word, and to support each other in their journey of faith.
Just as faith without works is shown to be dead or not a true faith (Jas. 2: 18-20), therefore anyone who has no desire to join a local Church is not part of the universal Church. The evidence of being part of the universal Church is shown in the desire and the act of joining a local Church and being a member in it. This is what we have interpreted the Church Father Cyprian to mean when he says, "Outside the Church there is no salvation." (Extra Ecclesium Nula Salus Est).
Since joining a church is necessary, we must find out which church to join. There are countless buildings and assemblies of people calling themselves churches, but does having the name "church" necessarily mean that these are true churches believers should join? Most certainly not!
Joining a church is supposed to be the expression of our membership in the universal Church. Therefore, all assemblies of people if they are to be true churches must be an expression of the universal Church. If any assembly of people do not exhibit the signs of a true church, they are not an expression of the universal Church and we should not join them.
The marks of a true church are: the proper proclamation of God's Word, the proper administration of the sacraments, and the right exercise of church discipline. By the proper proclamation of God's Word, we mean that the preacher preaches God's Word and explain the text of Scripture to us. If the preacher goes up and uses the Word of God as a launchpad to lecture on something that interests him but is not taught in the text of Scripture, that is not a proper proclamation of God's Word.
The sacraments are Baptism and the Lord's Supper. If any assembly that calls itself a church does not do these sacraments and them only, they are not properly administering the sacraments. Therefore, both the Roman Catholic church (with its 7 sacraments) and the Salvation Army (which do not administer any sacrament) are not true churches.
The third sign is the right exercise of church discipline. Positively, church discipline is exercised in discipleship of believers in the faith. Negatively, church discipline is exercised in rebuke, censor and as a last resort, excommunication of any unrepentant member who commits grievous sin. Many churches are liable to be disqualified on the basis of this third sign as they do not discipline members who commit grievous sin.
God calls us into the Church, and therefore we should seek out a true church and join it. In the church, we are in a place to be cared for and nourished by the Word of God, for the glory of God.