Impotent folk - Sick people; or people who were weak and feeble by long disease. The word means those who were “feeble” rather than those who were afflicted with “acute” disease.
Halt - Lame.
Withered - Those who were afflicted with one form of the palsy that withered or dried up the part affected. See the notes at Matthew 4:24.
Moving of the water - It appears that this pool had medicinal properties only when it was “agitated” or “stirred.” It is probable that at regular times or intervals the fountain put forth an unusual quantity of water, or water of special properties, and that “about” these times the people assembled in multitudes who were to be healed.