Charles H. Spurgeon on Psalms 20:3

"Selah." * This word, in the judgment of the learned, is sometime vox optantis, the voice of one that wisheth, equivalent to amen; of vox admirantis, the voice of one admiring, showing some special matter; or vox affirmantis, of one affirming, avouching what is said; or vox meditantis, of one meditating, requiring consideration of what is said. But withal, it is a rest in music. Jerome saith it is commutatio metri, or vicissitudo canendi. —Edward Marbury. * See pages 25, 29, 38. Psalm 3.