St. Irenaeus (d. 202AD) describes in theological metaphors and by example from life itself his own understanding of Holy Communion.
“‘Just as the wood of the vine, planted in the earth, bore fruit in its own time, and the grain of the wheat, falling into the earth and being decomposed, was raised up manifold by the Spirit of God who sustains all, then, by wisdom, they come to the use of men, and receiving the Word of God, become Eucharist, which is the body and blood of Christ; in the same way, our bodies, nourished by it, having been placed in the earth and decomposing in it, shall rise in their time, when the Word of God bestows on them the resurrection to the glory of God the Father, who secures immortality for the mortal and bountifully bestows incorruptibility on the corruptible [cf. 1 Cor. 15.53], because the power of God is made perfect in weakness [cf. 2 Cor. 12:9], that we may never become puffed up, as if we had life from ourselves, nor exalted against God, entertaining ungrateful thoughts, but learning by experience that it is from his excellence and not from our own nature, that we have eternal continuance, that we should neither undervalue the true glory of God nor be ignorant of our own nature, but should know what God can do and what benefits man, and that we should never mistake the true understanding of things as they are, of God and man.’
. . . It is by receiving the Eucharist, as the wheat and the vine received the fecundity of the Spirit, that Christians are prepared, as they also make the fruits into the bread and wine, for their own resurrection effected by the Word, at which point, just as the bread and wine receive the Word and so become the body and blood of Christ, the eucharist, so also will their bodies receive immortality and incorruptibility from the Father. Christians themselves, therefore, need to use the fruits of the world eucharistically, for it is by these that they are prepared for the resurrection and the gift of incorruptibility.” (John Behr, Asceticism and Anthropology in Irenaeus and Clement, pp 72-73)