لَيْسَ الْجِدُّ زِينَةً لِلْقَوْلِ، بَلْ هُوَ عَمَلٌ.
Serious effort is not decoration for words; it is action.
Laysa rejects a mistaken characterization; bal turns the listener to the preferred account. The construction is useful when an audience has confused sincere effort with elegant talk or slogans.
Not every occurrence of bal yields strict logical exclusivity. Its function here is correction and emphasis; the precise scope of any restriction must be assessed from context.