The Empty Oath and Where Repentance Can and Cannot Reach

Mekhilta DeRabbi Shimon Ben Yochai 20:7

"You shall not take the name of the LORD your God in vain" (Exodus 20:7): "vain" means nothing other than a thing that was not, and is not, and will never be. "For the LORD will not hold guiltless": since it was said at Horeb, "return, and I will hold guiltless," one might think that repentance atones; therefore it says, "for the LORD will not hold guiltless." Is this now a reasoning from the lighter to the heavier, such that repentance does not atone — only for a matter punishable by death at the hands of Heaven, or for every negative commandment in the Torah? Repentance does not atone; therefore it says, "for the LORD will not hold guiltless him who takes His name in vain" — for this, repentance does not atone, but it does atone for every other negative commandment in the Torah. This is now a reasoning from the lighter to the heavier: that repentance should atone for a positive commandment and for a negative commandment that contains the fulfillment of a positive one. Say from now on: whatever is from "you shall not take" and below are lighter transgressions, and repentance atones for them; and whatever is from "you shall not" and above are graver transgressions, and repentance does not atone for them. One might think that the Day of Atonement does not atone; therefore it says, "for on this day He shall atone for you" (Leviticus 16:30).

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