Indefiniteness can also signal a small or limited amount, the counterpart of multiplicity.
وَرِضْوَانٌ مِنَ اللَّهِ أَكْبَرُ
And approval from Allah is greater. (Al-Tawbah 9:72)
The Qur'anic wording does not literally say “a little approval.” That is one rhetorical explanation of its indefiniteness: even some divine approval surpasses the other blessings in value. Thus smallness in amount can coexist with supreme importance.