Rashi on Exodus 23:33/רש"י על שמות כ״ג:ל״ג

1כי תעבד וגו׳ FOR IF THOU SERVE etc. — Both particles כי in this verse have the meaning of אשר “that”. It has this meaning in several passages. This is really the sense of the Aramaic word אי (Hebrew אם) which itself is one of the four meanings in which כי is used (cf. Gittin 90a. where the four usages of כי are given). In fact we find אם (‎אי) used in many passages in the sense of אשר, e. g., (Leviticus 2:14) ואם תקריב where it certainly should not be translated “if” — but ”when thou offer an offering of thy first-fruits”, for this offering is not optional but is obligatory (cf. Rashi on that verse).