A modern choir sings a hymn in 3 minutes. Amish — in 20. One syllable can last 5-15 seconds. This isn't slow singing — it's a different kind of singing.
Why
Time belongs to God. Rushing means considering your time more important than His. Every syllable — prayer. Every note — breath. Stretching a word, you live it.
How It Sounds
To an outsider — strange. Monotonous. Droning. No melody (it seems). Actually there is melody — but winding, with melismas, intervals not found in modern music. Medieval chant, frozen in the 17th century and reaching our days alive.