فَبَشِّرْهُمْ بِعَذَابٍ أَلِيمٍ
So announce to them the “glad tidings” of a painful punishment.
In Qur’an 3:21, *bashshira* ordinarily introduces welcome news, but the accompanying ʿadhāb alīm names painful punishment. The reversal makes the threat and rebuke more forceful. The speaker is not promising something that would actually produce joy.
This is discussed as an opposing and ironical metaphor. The affirmative lexical surface is deliberately inverted by the punitive context. The phrase “painful punishment” functions as a direct indication that literal good news is not intended.