Not learning correct grammar could lead to disbelief
al-Asma’ee said,
تعلموا النحو فان بني اسرائيل كفروا بكلمة واحدة كانت مشددة فخففوها قال الله: يا عيسى اني ولدتك. فقرءوا: يا عيسى اني ولدتك. مخففا فكفروا
“Learn grammar for surely Bani Israa’eel disbelieved due to one word that [originally] contained a shaddah but then they removed it. Allah said,
‘O ‘Esaa indeed I brought you into existence [wal-lad-tuka]’
And they recited it as,
‘O ‘Esaa indeed I begot you [wa-lad-tuka]’
They removed the shaddah [on the laam] and disbelieved due to that.”
Source: Rawdatul ‘Uqalaa p. 222