The Importance of the Sciences of Ma‘ānī and Bayān for Ijtihād

Answer: What is required for ijtihād is mentioned in the principles of jurisprudence (uṣūl al-fiqh): such as commands and prohibitions, literal and metaphorical usage, general and specific expressions, and so on. Most chapters of uṣūl are linguistic, and in uṣūl al-fiqh they have laid down the fundamentals that the mujtahid must necessarily know.
What I see is that, even though they have placed within it everything the mujtahid needs, full comprehension of what it contains, as it ought to be understood, is not achieved except through firm grounding in the sciences of the Arabic language.
That is because the Qur’an and the Sunnah are Arabic, and proper knowledge of what is intended cannot be attained except by one who is knowledgeable in the language. For the structures of Arabic speech contain secrets that none can grasp except one firmly grounded in the sciences of the Arabic language, including the sciences of Ma‘ānī and Bayān.
Nothing caused the literalists to fall into adhering strictly to outward meanings except their ignorance of the secrets of the eloquence of the Arabic language.
In summary: the Qur’an and the Sunnah came in the language of the Arabs, and understanding what is intended by them depends upon knowing the Arabic language in all its aspects: vocabulary, grammar, and rhetoric.

Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.3