申命記 15:8 註釋：Rashi, Ibn Ezra, Rashbam & Or HaChaim

פתח תפתח [BUT] THOU SHALT SURELY OPEN [THINE HAND] — even many times (Sifrei Devarim 116:13).

You must open employs a verbal noun. In fact, every verb that is not preceded by the verbal noun is in reality an elliptical construct. But the homiletical explanation [Bava Meṣi‘a 31b] [that it applies to the poor of other cities as well as to of one’s own — Translator] is also attractive.

כי פתוח תפתח את ידך, but

כי פתח תפתח BUT THOU SHALT SURELY OPEN [THINE HAND] — Here, you see, the word כי has the meaning of “but” (whilst e.g.. in v. 7 it means “if”, in v. 10 “because”).