وَيْلٌ لِكُلِّ هُمَزَةٍ لُمَزَةٍ
Woe to every habitual fault-finder and defamer. (الهمزة: 1)
Waylun is an indefinite noun placed at the outset as a strong warning. Li-kulli extends the statement to anyone bearing the condemned traits rather than limiting it to a named individual. The expression therefore turns attention from a single person to a recognizable pattern of conduct.
Indefiniteness and generality must not be collapsed into one rule: the indefinite warning and the quantifier kull contribute distinct effects that cooperate in this context.