The purpose of the Lord’s Supper is to inspire, confirm, and nourish faith; however, the the Lord’s Supper does this ministerially. From an inward standpoint, it is the Holy Spirit who sparks and inflames faith in our hearts. Thus, we must distinguish between the outward, public, and ministerial role of the Lord’s Supper and the the more intimate and personal role of the Holy Spirit.
To see the relationship between the Spirit and the Supper, consider the function of our human eyes and human ears. Just as the eyes can only see by the brightness of the Sun and just as the ears can only hear by the sound of another human voice, so it is also true that this brightness can only be detected because the seer has been endowed with sharpness of vision, having the capability of being illumined. In the same way, the ears of the hearer would never be struck by any noise unless they were created and fitted for hearing.
What the facility for sight does for our eyes and what the capacity of hearing does for our ears are both analogous to what the Holy Spirit does in our hearts that faith be conceived, sustained, nourished, and established in our hearts. What this means is, first, being blessed by the Lord’s Supper is primarily a matter of the objective act of blessing on God’s part, namely God’s redemptive work in Christ. Second, being blessed is a matter of subjective appropriation of that divine act of blessing. This subjective appropriation is a matter of the work of the Holy Spirit who gives us the ability to hear and see spiritually. If the Holy Spirit were absent, the Lord’s Supper can accomplish nothing more in our minds that the brightness of the sun shining upon blind eyes or a voice sounding in deaf ears. The ministry of the Eucharist is empty apart from the action of the Spirit, but the Lord’s Supper is charged with great effect when the Spirit works within and manifests His power.
The sacraments have the same office as the Word of God, namely, to offer Christ and the treasures of heavenly grace He promises. To be united to Christ in covenantal fellowship is how we receive the gifts of grace. It is the faith relationship to Christ which brings everything else. Word and sacrament offer Christ and His blessings, whereas faith accepts the offer. In other words the sacraments are of no benefit unless the Holy Spirit accompanies them. Consider the words of John Calvin on this matter:
For He it is who opens our minds and hearts and makes us receptive to this testimony. In this also, varies and distinct graces of God brightly appear. For the sacraments are for us the same thing from God, as messengers of glad tidings or guarantees of the ratification of covenants are from men. They announce and tell us, and ratify among us, those things given to us by divine bounty. The Holy Spirit is He who brings the graces of God with Him, gives a place for the sacraments among us, and make them bear fruit.
Indeed God is with us and is present in the Lord’s Supper by the very present power of the Holy Spirit. For this reason, heavy weight should be placed not on the outward forms of the celebration, but on the inward communion between Christ and His people. Beyond the symbols, Christ is immediately present to those who believe His Word. He is present by the power of an in the person of the Holy Spirit, who is both the power of God and the bond of love between the Father and the Son. That is, believers are united to Christ in the same way the Son is united to the Father – by the bond of love who is the Holy Spirit.