Albert Barnes Commentary Lamentations 2:18

"Their heart cried unto the Lord: O wall of the daughter of Zion, let tears run down like a river day and night; Give thyself no respite; let not the apple of thine eye cease." — Lamentations 2:18 (ASV)

Their heart - That of the inhabitants of Jerusalem. The prophet bids the wall, as the representative of the people who had dwelt secure under its protection, shed floods of tears on their behalf. Broken up by the enemy, it could be their guardian no longer, but by its ruins it might still cry to the Lord on their behalf.

A river - Or, a brook or torrent.

Rest - Properly, the torpor and numbness which follows excessive grief.

Apple of your eye - See Psalms 17:8 note.