레위기 26:18 해설: Rashi, Kli Yakar, Or HaChaim & Rashbam

ואם עד אלה means AND IF, WHILE THESE ARE YET with you,לא תשמעו YOU WILL NOT HEARKEN,

Seven for your sins. There is reason to consider that three times it says for your sins, and one time it inserts in the middle seven like your sins. There are also changes in language in these four places, and certainly these were not casual variations. It appears that initially it says seven for your sins corresponding to the seven sins that Rashi enumerated, and it says that the punishments will not be directly measure for measure, because each type adheres more to its own kind than to a different kind. Therefore, God in His mercy did not want the punishment to be of the same type as the sin, so that the punishment would not adhere to them strongly when similar types meet.
However, afterward it says, If you walk with Me by chance. And you say that it is surely a coincidence for you and not that the hand of God did this, because you see that the punishments are not of the same type as the sin, I will add to you a punishment seven like your sins. This is precisely measure for measure, so that you will believe that it is not the snake that kills, but the sin that kills (Berakhot 33a). And if by these you are not disciplined, such that you brazen your faces to say in any case that it is a coincidence for you, and it will not help that I have seen to direct the punishments towards your sins, then I too will walk with you by chance. Because until now I have not left you to chance occurrences, and I chastised you Myself as a man disciplines his son, but since God does these things twice, three times with a man (Job 33:29) and it does not help, from now on I will abandon you to chance, and then the punishments will necessarily be seven for your sins. Not like your sins, because chance does not operate with providence to direct punishments corresponding to sins, and the number seven is also not providential, rather if all seven planets that operate by chance will affect you adversely, therefore they will be seven in number. And what is said, I will also strike you, this is not an actual direct blow, but rather this blow from Me is that I will abandon you to the chances of time, and they will affect you with evils without mercy, for there is no mercy in chance.
But nevertheless, the matter is still in doubt, for perhaps chance will bring them good and it is not a certainty. Therefore it says, And if with this you will not listen to Me. And you will say in any case that it is a coincidence for you, I will walk with you with the fury of chance. It adds with the fury because I know how to time it when the celestial arrangement is in fierce, poured-out anger, and at that time I will make it rule over you, and then it will certainly affect you with evils without doubt.

לא תשמעו לי, "you do not listen to Me." Teshuvah is made conditional on "listening" to G'd, i.e. studying Torah. True repentance is impossible without Torah study.

ויספתי — This together with ליסרה means, THEN I WILL ADD still other afflictions,