Charles Ellicott Commentary Leviticus 26:18

"And if ye will not yet for these things hearken unto me, then I will chastise you seven times more for your sins." — Leviticus 26:18 (ASV)

And if you will not yet for all this hearken unto me. —Better, and if up to these you will not hearken unto me, that is, if they should persist in their disobedience to the very end of those punishments mentioned in Leviticus 26:16-17. This verse, therefore, introduces the second degree of punishments, which ends with Leviticus 26:20.

I will punish you seven times more. —That is, indefinitely or unceasingly; many more times. Seven being a complete number is often used to denote thoroughness (see Note on Leviticus 4:6), a large or indefinite number. Hence the declaration He shall deliver you in six troubles; yea, in seven there shall no evil touch you (Job 5:19), and if he trespass against you seven times in a day (Luke 17:4), that is, an indefinite number of times. (Proverbs 24:16, etc.)