A threefold purpose might be considered:
1. It functions as a memory aid, because each poetic verse begins with a new letter of the Hebrew alphabet.
2. A complete alphabet conveys the fullness and depth of lament, “from A to Z.”
3. The use of acrostics enables the poet to devote his full attention to the theme at hand.1
1 Eh quoi! elle est assise solitaire, cette ville si peuplée! Elle est semblable à une veuve! Grande entre les nations, souveraine parmi les Etats, Elle est réduite à la servitude!