On the cross, Jesus Christ became sin in humanity’s place, although he had never known sin, in order that individuals might overcome death with the righteousness of Christ (2 Corinthians 5:21). His vicarious death forgives and rids people of sin in order to have a right relationship with the Father. They are justified, redeemed, reconciled, and adopted. This is the church: the communion of saints gathered to worship God and witness in the world to his glory.
But when God saves an individual, he does not reconcile that person to himself alone. He reconciles a people to himself and to each other. As adopted children of God, they become brothers and sisters to one another. God creates a new community, a family, in Christ.
Organism: One Body
Although consisting of individuals, the church is best recognized as a single entity or organism — the Body (Romans 12:5; 1 Corinthians 12:12-31) and Bride (John 3:29; Revelation 19:7) of Christ — diverse in its members, but unified in “one Spirit…one Lord, one faith, one baptism, one God and Father of all, who is over all and through all and in all” (Ephesians 4:5-6). Without this spiritual unity, the church cannot exist. In the Spirit, who applies the saving work of Christ to our lives, God unites people of all ethnicities, races, classes, genders, personalities, and abilities to himself and to one another, establishing this new family by and in his love (Galatians 3:28).
Institution: Structured Body
While the church is not a building or hierarchy, it is incorrect to assume that spiritual unity can occur without some form of institutional or external unity as well, although the Spirit does indeed bear witness to our salvation internally (Romans 8:16). When Christ instituted his church, he intentionally built it upon the foundation of the prophets and apostles (i.e. Scripture, the Word of God), himself being the cornerstone of that foundation (Ephesians 2:20). A church that is not subject to the Word is not the Christian church, for it is not subject to Jesus Christ. The Spirit unites us in Christ primarily by his Word.
Moreover, by his good pleasure, the Spirit is present to us in the sacraments, baptism and communion (also called the Lord’s Supper or Eucharist), structural elements of the church which Scripture identifies in Jesus’ express command for the church (Matthew 28:19; Luke 22:14-23). Additionally, Scripture teaches that the Spirit calls and enables certain members of the church to serve in offices or leadership positions, such as teacher, elder, or deacon (Ephesians 4:11-12; 1 Timothy 3:1-13) who shepherd the church according to the Word of God until Jesus returns. With the Spirit accompanying these institutional aspects of the church, God spiritually unifies his people.
In the church, God has initiated his kingdom here on earth. In that sense, it is like a pearl of great price (Matthew 13:45-46), something good and beautiful in itself, not simply a means to some end. With Christ as the head of this Body and the groom of this Bride, we relate to God most intimately as we worship him, individually and corporately, internally and externally.
But this kingdom is not yet complete. The church is tasked with the mission of witnessing to the world that Christ has come to save and establish his kingdom. The church accomplishes this mission in two ways. One, it stands against culture as a new, familial community, a witness to the coming kingdom, inviting others to this intimate relationship with our Creator and Father. Two, it engages culture as redeemed persons enter into their daily lives having been transformed by the work of Christ, living in the knowledge that he is indeed Lord over all aspects of life. In this sense, the church is like a light to the world and salt to the earth (Matthew 5:13-16), a force set on restoring the world.