Our very own Heidelberg Catechism question 55 asks, “What do you understand by ‘the communion of saints?’” The answer expresses the unity of the church,
First, that all and every one, who believes, being members of Christ, are in common, partakers of him, and of all his riches and gifts;a secondly, that every one must know it to be his duty, readily and cheerfully to employ his gifts, for the advantage and salvation of other members.b
This attribute of the church concerns our union with Jesus Christ. As we are increasingly clothed in Christ in sanctification, we more and more desire to serve our brothers and sisters in Christ. No doubt, God receives more and more glory as we recognize our duty. Unity then shows that God gets more glory in the communion of believers through the one and same Spirit than in private devotion (1 Cor. 6:17, 19; 12:13; 2 Cor. 12:18; Eph. 4:4). The Spirit brings the church together as members in Christ. We, therefore share one faith, hope, love and baptism to the glory of the Lord (Eph. 4:3–5). True religion is not purely spiritual membership, the error of the Anabaptist, nor is it mere identification with an institutional church, the error of Rome. Christianity is a spiritual body united together by the Holy Spirit and Word as an organism that organizes to worship corporately. Our union with Christ is all about our relationship with God that flows out to others. Religion then is not purely individual and private. There are no Lone Ranger’s in the church, for Christianity is corporate unity. Mere private devotion cannot bring the glory to God that unified corporate worship brings. Mere private devotion is not Christianity. The next attribute, catholicity, attests to this fact, stayed tuned.
a 1 John 1:3; 1 Cor. 1:9; Rom. 8:32; 1 Cor. 12:12, 13; 1 Cor. 6:17.