“Moreover, Christ is the only food of our soul, and, therefore, our heavenly Father invites us to him, that, refreshed by communion with him, we may ever and anon gather new vigour until we reach the heavenly immortality. 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, nay, by giving, as it were, earnests and badges, he makes it as certain to us as if it were seen by the eye; the familiarity of the similitude giving it access to minds however dull, and showing that souls are fed by Christ just as the corporeal life is sustained by bread and wine. …
Pious souls can derive great confidence and delight from this sacrament, as being a testimony that they form one body with Christ, so that every thing which is his they may call their own. Hence it follows, that we 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 imputed to himself as if they were his own. This is the wondrous exchange made by his boundless goodness.”
[John Calvin, Institutes of the Christian Religion, 4.17.1]
