«فَلَا يَخْدَعَنَّكَ لُمُوعُ السَّرَابِ»
Do not let the glitter of a mirage deceive you.
The prohibitive form is strengthened by emphatic morphology. A plain “do not be deceived” is intelligible, but the Arabic carries the urgency of a firm warning. The mirage is an appearance of water, not a reliable source.
The setting is the allure of public office. Rendering the mirage as a real oasis undermines the very comparison. Translate both halves of the force: the glittering appearance and the speaker's warning not to mistake it for lasting substance.
Translation exercise
Translate both the emphatic prohibition and the unreliability of the mirage in one line.