Chazal's requirement: verses not according to the written plain text

Hello,
Chazal often use, for the purposes of Haggadah and Halacha, the simple meaning of a word as in the verse, for example, "Do not call your children your builders."
"They will buy fields for money" Chazal changes "they will buy" with a fatah instead of a hirik as it is in the original – and all this in order to adapt the halakha they have to the verse
Is there a logical explanation for these moves? If not, then why is it needed? Let them say, for example, that's how it was done and that's it.
thanks!