An expression can be used in relation to its opposite to produce irony or reproach. This requires an indicator of the intended reversal, not an arbitrary inversion of meaning.
«فَبَشِّرْهُمْ بِعَذَابٍ أَلِيمٍ»
Give them the glad tidings of a painful punishment.
“Glad tidings” ordinarily concerns welcome news; accompanying “painful punishment” makes the ironic or mocking purpose evident. The audience does not take gladness as the actual message.
The relation of opposition, the contextual signal, and the communicative purpose must be separated.