Some good thoughts on the Lord’s supper from Institutes of the Christian Religion by John Calvin…

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But as this mystery of the secret union of Christ with believers is incomprehensible by nature, he exhibits its figure and image in visible signs adapted to our capacity….  We now, therefore, understand the end which this mystical blessing has in view–namely to assure us that the body of Christ was once sacrificed for us, so that we may now eat it and feel within ourselves the effective power of that one sacrifice; that his blood was once shed for us so as to be our perpetual drink. This is the force of the promise which is added, “Take, eat; this is my body, which is broken for you” (Matt. 26:26). The body which was once offered for our salvation we are encouraged to take and eat.  While we see ourselves made partakers of it, we may safely conclude that the virtue of that death will be effective in us.  Hence he terms the cup the covenant in his blood.  For the covenant which he once sanctioned by his blood he in a manner renews, or rather continues, in so far as regards the confirmation of our faith….

Pious souls can derive great confidence and delight from this sacrament, as being a testimony that they form one body with Christ, so that everything which is his they may call their own.  [W]e can confidently assure ourselves, that eternal life, of which he himself is the heir, is ours, and that the kingdom of heaven, into which he has entered, can no more be taken from us than from him; on the other hand, that we cannot be condemned for our sins, from the guilt of which he absolves us, seeing he has been pleased that these should be attributed to himself as if they were his own.  This is the wondrous exchange made by his boundless goodness.  Having become with us the Son of Man, he has made us with himself sons of God.  By his own descent to the earth he has prepared our ascent to heaven.  Having received our mortality, he has bestowed on us his immortality.  Having undertaken our weakness, he has made us strong in his strength.  Having submitted to our poverty, he has transferred to us his riches.  Having taken upon himself the burden of unrighteousness with which we were oppressed, he has clothed us with his righteousness.