You have often been reminded that in this meal we partake of the body and blood of Jesus Christ. We do not do this because He is somehow locally present on this Table—for He is at the right hand of the Father, and not here. But Paul is very clear that we are made partakers of His table (1 Cor. 10:21). This cup is the communion of the blood, and this bread is the communion of the body (1 Cor. 10:16). So we know that it happens, but how does it happen?
The historic Reformed reply is that we are joined together with Christ, knit together with Him, and joined to Him, by means of the Holy Spirit’s work. This is what the Holy Spirit does for us. If a man does not have the Spirit of Christ, then he is none of Christ’s (Rom. 8:9). And if Christ is in you, even though your body is mortal (because of sin), the Spirit in you is still life, and communicates that life to you (Rom. 8:10). If the Holy Spirit, the one who raised Jesus from the dead, dwells in you, then He will be engaged in quickening your mortal body (Rom. 8:11). As He does this, He is knitting you together with Christ.
This means that your participation in Christ, and His indwelling of you, is established, strengthened and completed by means of God’s Holy Spirit. The Spirit is the one who accomplishes this great physical renewal. He is the one who takes all the means of grace that the Father has established, and applies it to you, both body and soul. He uses the ministry of the Word, and the ministry of the sacraments, to grow you up into Christ. So come, therefore, to eat and drink.