In the Bible, an altar is usually made of fitted stones, and animals are sacrificed and burned there (Genesis 8:20, Leviticus 1:1-9). A table is a flat surface, commonly made of wood, the kind of place where people sit to eat a meal.

During the celebration of the Eucharist, what does the officiant do? That question formed part of the polemic of the Reformation. The prevalent Roman Catholic view of what happens during the mass was that the priest offers the body of Jesus as a sacrifice to God, on the church altar right now. Our Reformation ancestors rejected this idea, and insisted that Jesus had offered himself as a sacrifice once for all, at one unrepeatable moment of history (Romans 6:10, Hebrews 9:28, 10:12, I Peter 3:18). So Presbyterians say the Lord’s Supper is a meal served at a table, where we are spiritually fed by Jesus with these symbols of his life given for us.

Thus our heritage teaches us to call the piece of furniture at the front of the chancel a table rather than an altar.

Except sometimes we don’t. People often speak colloquially. That’s what you did, when you asked about flowers on the altar. You probably weren’t looking for a theology lesson; you just wanted to know where to put the flowers. If your minister had perceived that, he might have saved the exhortation for another time.