Комментарий к Шмот 9:21

ואשר לא שם לבו…ויעזב, and whoever paid no heed…left his cattle outdoors, etc. The extra letter ו in ויעזב, is to draw to our attention that those people who had up to now refused to heed G'd's warning added to their previous sin by continuing in their ways, deliberately exposing their livestock and servants to death by hail despite G'd's warning. Their obstinacy was such that though they could have saved their property by the simple expedient of bringing it indoors for a while, they defied G'd and did not do so. It is clear from the Torah's report that what motivated the Egyptians was not so much their economic need of the cheap labour that the Israelites represented and which made them refuse to liberate them, but their defiance of the Jewish G'd. Even those who doubted G'd's ability to orchestrate a plague of hail such as Moses had predicted preferred to demonstrate their defiance by risking their property. Perhaps the reason they took such a chance was that the previous six plagues had not been severe enough so that they did not believe that G'd could suddenly bring such a terrible plague.

ואשר לא שם לבו חטא ויעזוב, it would become clear that he who sinned paid with his life. This is why I warn you now to save your lives.

“and whoever did not take the word of G-d to heart” – even those who did not fear G-d had cattle if they did not take their animals unto the fields on the day of the plague of the Epidemic.