The science of qirāʾāt examines established forms of Qur'anic recitation and the precise realization of words. Tafsir investigates the intended meanings signified by those words. Both serve the Qur'an, but their direct questions differ.
An established variant reading may sometimes affect interpretation, and the commentator must consider it where relevant. Yet describing a word's pronunciation does not by itself provide a complete explanation of its meaning.
The distinction helps organize Qur'anic studies: reliable transmission and recitation establish the text, while tafsir investigates its indication of meaning.