Jesus gave his followers two signs, or sacraments, to strengthen them in their faith: baptism and communion (the Lord's Supper). Calvin gives a helpful definition of a sacrament:

[I]t is an outward sign by which the Lord seals on our consciences the promises of his good will toward us in order to sustain the weakness of our faith; and we in turn attest our piety toward him in the presence of the Lord and of his angels and before men (Institutes, 4.14.1).

In other words, the Lord makes promises, we receive those promises by faith (piety), and as we perform the outward sign, the Lord says a big "Yes!" to his promises to us.

So what are the promises to which God is saying "Yes!" as we take the Lord's Supper?

[W]hen bread is given as a symbol of Christ's body, we must at once grasp this comparison: as bread nourishes, sustains, and keeps the life of our body, so Christ's body is the only food to invigorate and enliven our soul. When we see wine set forth as a symbol of blood, we must reflect on the benefits which wine imparts to the body, and so realize that the same are spiritually imparted to us by Christ's blood. These benefits are to nourish, refresh, strengthen, and gladden (Institutes, 4.17.3).

God has promised that the death of his Son is sufficient for us, to sustain us, to give us life and to keep us alive, and to give us strength and joy in following him. So when that promise is proclaimed, and when that promise is believed, then, in the very act of eating and drinking, God says a big "Yes!" to those promises. And what is the effect on us as we eat and drink in this way? Each and every time we take communion and each and every time God says his big "Yes!" to his promises, we are spiritually fed: our faith is strengthened, our hearts rejoice and our inner being is nourished. In other words, the Lord's Supper is one of the ways in which, spiritually, we feed on Christ by faith.

What a privilege to be able to share communion together!