7th Century
St. Isidore of Seville
Late Patristic
St. Isidore of Seville (c. 560 – 636), Archbishop of Seville and Doctor of the Church. Wikipedia
"The bread, because it strengthens the body, is thus called the body of Christ. The wine, because it acts on the blood in the body, is therefore referred to as the blood of Christ. However, although these things are visible, nevertheless, sanctified through the Holy Spirit, they pass over into the sacrament of the divine body. "
On Ecclesiastical Offices
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Why this quote matters
Liturgical practice and symbolic explanation of Eucharistic elements.
Source citation: On Ecclesiastical Offices.