וּבָ֧א עָלַ֣יִךְ רָעָ֗ה לֹ֤א תֵדְעִי֙ שַׁחְרָ֔הּ וְתִפֹּ֤ל עָלַ֙יִךְ֙ הֹוָ֔ה לֹ֥א תוּכְלִ֖י כַּפְּרָ֑הּ וְתָבֹ֨א עָלַ֧יִךְ פִּתְאֹ֛ם שׁוֹאָ֖ה לֹ֥א תֵדָֽעִי׃
Yet shall evil came upon thee; Thou shalt not know how to charm it away; And calamity shall fall upon thee; Thou shalt not be able to put it away; And ruin shall come upon thee suddenly, Before thou knowest.
Rashi on Isaiah
you shall not know how to remove it by prayer Heb. לֹֹא תֵדְעִי שַׁחְרָהּ. You shall not know to pray about it (Jonathan). Whom will you beseech to extricate you therefrom?
Ibn Ezra on Isaiah
יום רעה═רעה A day of evil.15A. V., Evil. I. E. supplies יום the day of because of the masculine form of the verb ובא.
Rashi on Isaiah
to rid yourself of it Heb. כַּפְּרָהּ, to wipe it away and to remove it, and this is every expression of atonement (כַּפָּרָה). It is an expression of wiping and taking away.