A.T. Robertson Commentary Matthew 19:8

"He saith unto them, Moses for your hardness of heart suffered you to put away your wives: but from the beginning it hath not been so." — Matthew 19:8 (ASV)

For your hardness of heart (προς την σκληροκαρδιαν υμων). The word is apparently one of the few Biblical words (LXX and the N.T.). It is a heart dried up (σκληρος), hard and tough.

But from the beginning it hath not been so (απ' αρχης δε ουκ γεγονεν ουτως). The present perfect active of γινομα to emphasize the permanence of the divine ideal. "The original ordinance has never been abrogated nor superseded, but continues in force" (Vincent). "How small the Pharisaic disputants must have felt in presence of such holy teaching, which soars above the partisan view of controversialists into the serene region of ideal, universal, eternal truth" (Bruce).