Perhaps Psalm 91 was sung antiphonically; that is, one person may have sung first, with a choir responding.
بعدئذ يُسمَع على الارجح صوت مرنِّم واحد (‏ ٩١ :‏ ٩ أ‏ )‏ وتجيبه فرقة (‏ ٩١ :‏ ٩ ب -‏ ١٣‏ )‏ .‏