Just as He called the world into being by the power of His Word (Ps. 33:6–9; Heb. 11:3), so God brings His church into being by the power of the gospel call (2 Thess. 2:13–14; 1 Peter 2:9–10). That calling summons us into union with Christ by faith, as one people under the triune God (Eph. 4:4–6). The church is defined by our calling into fellowship with Christ and with one another, as Paul reminds the Corinthians: "Unto the church of God which is at Corinth, to them that are sanctified in Christ Jesus, called to be saints. . .. God is faithful, by whom ye were called unto the fellowship of his Son Jesus Christ our Lord" (1 Cor. 1:2a, 9; KJV here and throughout).
Communion with God in Christ is the heart of experiential Christianity. The fullness of the church's joy is to have fellowship with one another and with the Father and the Son (1 John 1:3–4). Because of our union with Christ as members of His body, the church (Eph. 1:22–23), the Spirit of Christ who dwells in Christ the head dwells in all His members (Rom. 8:9).
The indwelling Spirit is the essence of our communion with the Father and the Son (2 Cor. 13:14; Eph. 2:18). John Calvin said, "The Holy Spirit is the bond by which Christ effectually unites us to himself" (Institutes 3.1.1). As husband and wife are "one flesh," we are "one spirit" with the Lord Jesus (1 Cor. 6:16–17). Imagine how close you would be to a friend if your very soul could dwell in him. Such is Christ's intimacy with each of His members through the indwelling Holy Spirit. This same Spirit baptizes us into the one body of Christ, uniting us in faith, life, worship, and service (1 Cor. 12:12—13; Belgic Confession, Article 27).
Therefore, it should come as no surprise that the sacraments of the church confirm and manifest our union with Christ and with each other. Galatians 3:26–28 says:
For ye are all the children of God by faith in Christ Jesus. For as many of you as have been baptized into Christ have put on Christ. There is neither Jew nor Greek, there is neither bond nor free, there is neither male nor female: for ye are all one in Christ Jesus.
Galatians 3:26 clearly says that we are saved by faith, not by any of our works, whether moral works such as keeping the Ten Commandments or ceremonial works such as circumcision, baptism, or the Lord's Supper (see also 2:16; 5:2). Yet verse 27 says that those who have been baptized "have put on Christ" and, therefore, are "one in Christ." How is this to be understood? They are to look to their baptism not as a cause but as a sign of their union with Christ by faith and, in Him, with each other. In his 1545 Catechism, Calvin sets forth this definition:
What is a sacrament? An outward attestation of the grace of God which, by a visible sign, represents spiritual things to imprint the promises of God more firmly in our hearts, and to make us more sure of them. (Q. 310)
If the sacrament of baptism itself united us to Christ and saved us, it would be inconceivable for Paul to write that "Christ sent me not to baptize, but to preach the gospel" (1 Cor. 1:17). Why preach the gospel if the desired results could be obtained simply by baptizing all people? The gospel, not baptism, is "the power of God unto salvation" (Rom. 1:16). Calvin said:
We are not to be taken up with the earthly sign so as to seek our salvation in it, nor are we to imagine that it has a peculiar power enclosed within it. On the contrary, we are to employ the sign as a help, to lead us directly to the Lord Jesus, that we may find in Him our salvation and . . . well-being. (Catechism Q. 318)
Thus, Paul warns us in 1 Corinthians 10:1–4 that we can receive the sacraments but still be unbelieving, unconverted, and, ultimately, rejected by God:
Moreover, brethren, I would not that ye should be ignorant, how that all our fathers were under the cloud, and all passed through the sea; and were all baptized unto Moses in the cloud and in the sea; and did all eat the same spiritual meat; and did all drink the same spiritual drink: for they drank of that spiritual Rock that followed them: and that Rock was Christ. But with many of them God was not well pleased: for they were overthrown in the wilderness.
Notice how he alludes to the new covenant sacraments by speaking of baptism, eating, and drinking. Sacraments do not and cannot save.
Does this mean that baptism and the Lord's Supper are only ceremonies of remembrance? By no means. The Apostles often exhort believers to look back on their baptism as a sign of their union with Him who died and rose again (Rom. 6:3–4; Gal. 3:27; Eph. 5:25–26; Col. 2:12; 1 Peter 3:21–22). The bread we break and the cup we bless are the communion of the body and blood of Christ (1 Cor. 10:16). Used in faith, they are means of drawing near to Christ, to access the benefits of His atoning work, applying it to ourselves and finding grace to live for God (Rom. 6:1–14).
The sacraments are a means by which Christ, through His Spirit's work, offers Himself to us to be received by faith. That is why Paul spoke of receiving "spiritual" food and drink from Christ (1 Cor. 10:3–4), of being baptized by the Spirit and being made to drink of the Spirit (12:13), as well as being filled with the Spirit (Eph. 5:18).
Calvin wrote, "If the Spirit be lacking, the sacraments can accomplish nothing" (Institutes 4.14.9). Moreover:
The Spirit in very truth is the only One who can touch and move our hearts, enlighten our minds, and assure our consciences; so that all this ought to be judged as His own work, that praise may be ascribed to Him alone. Nevertheless, the Lord Himself makes use of the Sacraments as inferior instruments as it seems good to Him, without in any way detracting from the power of His Spirit. (Catechism Q. 312)
When the church assembles in Christ's name and celebrates the Holy Supper in remembrance of Him, we have real communion or spiritual fellowship with Christ. Notice the repetition of the word "communion" (from the Greek koinōnia: "fellowship, partaking or sharing in common") in various forms in 1 Corinthians 10:16–20:
The cup of blessing which we bless, is it not the communion of the blood of Christ? The bread which we break, is it not the communion of the body of Christ? For we being many are one bread, and one body: for we are all partakers of that one bread. Behold Israel after the flesh: are not they which eat of the sacrifices partakers [koinōnoi] of the altar? What say I then? That the idol is any thing, or that which is offered in sacrifice to idols is any thing? But I say, that the things which the Gentiles sacrifice, they sacrifice to devils, and not to God: and I would not that ye should have fellowship [koinōnous] with devils.
What did Paul mean by saying that partaking of the bread and the cup is the "communion" of the body and blood of Christ? In part, he meant that we are thereby joined together as "one body" (v. 17). We have fellowship one with another. But there is more. Calvin said, "But whence, I [ask] you, comes that koinōnia (communion) between us, but from this, that we are united to Christ?" (commentary on 1 Cor. 10:16).
Paul uses the same language of koinōnia with respect to Old Testament worshipers. Eating the sacrifices, they had communion in the altar. They shared a meal with God on the basis of blood sacrifice and through an ordained priesthood. The church shares a covenantal meal with the Lord, feasting in His presence upon blood-bought grace.
Paul also used the same language of pagan worshipers: they have communion with demons. They worship in the presence of unclean spirits. Paul is saying that worshipers actually connect with the fallen beings they worship. If we participate with demons, it is a form of spiritual adultery that provokes God's jealousy (v. 22). Obviously this "communion" is a spiritual reality of great significance. Paul sets this pagan worship in direct contrast to the Lord's Supper, obviously wanting us to see them as parallels (v. 21).
Thus, we see what Paul means by "the communion of the blood of Christ" and "the communion of the body of Christ." We renounce the powers of Satan and have spiritual fellowship with Christ Himself, crucified for us, and now risen and exalted as our heavenly Head and High Priest. We feast on the benefits of His atoning death and the power of His endless life. Calvin said that the Supper is "a spiritual banquet, wherein Christ attests himself to be the life-giving bread, upon which our souls feed unto true and blessed immortality [John 6:51]" (Institutes 4.17.1).
Let us value the sacraments as "precious ordinances of God" to be used by faith in Christ. If we use them as "hypocrites, in whom the mere symbol awakens pride," our confidence is misplaced, and the physical symbols are empty. But if we receive them as those who are joined to Christ by true faith, we see "the promises which they exhibit of the grace of the Holy Spirit" (Calvin's commentary on Gal. 3:27), and, by faith, Christ will dwell increasingly in our hearts (Eph. 3:16–17).