You can’t reason about anything until you can see what the words are actually doing.
In the trivium, grammar wasn’t a checklist of rules for correct speech. It was the discipline of understanding how language constructs meaning at all — how a word’s origin, structure, and use shape what it can and can’t say, and how that structure can be bent to mislead as easily as to inform. It came first because everything built on top of it, logic and rhetoric included, depends on language actually meaning what it claims to.
Medieval grammar instruction, particularly from the early medieval period onward, developed its own substantial scholarly tradition around exactly this — treating the discipline as the necessary gateway skill for reading scripture, law, and philosophy correctly, not as rote memorisation.
Source: Luhtala, A. “Early Medieval Grammar.” In Concise History of the Language Sciences (Elsevier).