Do not forgive me with such indifference, lest I myself declare that punishment is due. The speaker implies that an insincere pardon is less desirable than a just consequence.

This couplet beautifully expresses a deep emotional truth. It's like saying, 'Please don't forgive me with such coldness or indifference that it makes me feel even worse than if I were punished.' The speaker would rather face a just punishment, because that would at least acknowledge the gravity of their action. Such an unfeeling pardon, given without warmth or sincerity, feels like a greater burden than any penalty. It highlights the pain of receiving forgiveness that lacks genuine care, making one wish for a consequence that feels more honest than a heartless pardon.