Rashi on Leviticus 26:21/רש"י על ויקרא כ״ו:כ״א

1ואם תלכו עמי קרי — Our Rabbis said (Sifra, Bechukotai, Chapter 5 5): this word signifies “irregularly”, “by chance” (מקרה), which is a thing that happens only occasionally; thus this means: if you will follow the commandments irregularly. Menachem explains it as an expression for “refraining”. Similar is, (Proverbs 25:17) “Refrain (הוקר) thy foot [from thy neighbour’s house]”; (Proverbs 17:27) “of a refraining (יקר) spirit”. This meaning approximates to the translation given by Onkelos which is a term denoting “stubbornness” (קושי) — that they harden their hearts so as to refrain from coming near unto Me.

2שבע כחטאתיכם SEVEN ACCORDING TO YOUR SINS — i. e. seven other punishments. These words mean: I will bring upon you more plagues (ויספתי עליכם מכה) in number, seven, corresponding to your sins (Sifra, Bechukotai, Chapter 5 5).