Sin is relative to one's spiritual level

בת ק' כבת כ' לחטא.

"At a hundred years she was like twenty regarding sin" (Rashi, Bereishis 23:1).

Rashi, explaining the verse about Sarah's years, teaches that at one hundred Sarah was as free of sin as a twenty-year-old. The Sefas Emes will probe what this comparison means.

וקשה אף שאינה בת עונשין מ"מ הדמיון הוא להיות נקוי' מחטא באמת.

And it is difficult: even though a twenty-year-old is not subject to Heavenly punishment, nevertheless the comparison is meant to indicate being truly cleansed of sin.

The Sefas Emes raises a problem. The usual point is that at twenty one is not yet liable to the Heavenly court — but Rashi's intent is deeper: that Sarah was genuinely pure of sin, not merely exempt from punishment. So the comparison needs explaining.

אך נראה דודאי אין צדיק בארץ כו' ולא יחטא רק שיש מדריגות רבות.

But it appears that certainly "there is no righteous person on earth who does good and does not sin" (Koheles 7:20) — only that there are many levels.

Since Scripture says no human being is entirely without sin, "free of sin" cannot mean absolutely flawless. Rather, sin and purity exist on a graded scale with many levels.

וכמו קודם זמן עונשין אין נחשב לו החטא שאין בו דעת שלימה לשמור מחטא כן יש חטאים שאין נחשבין לחטא ומצינו לעתיד ג"כ החוטא בן מאה שנה יקולל.

And just as before the age of punishment a sin is not reckoned to a person, since he does not have complete understanding (da'as sheleimah) to guard himself from sin, so too there are sins that are not reckoned as sins; and we likewise find regarding the future, "the sinner at a hundred years shall be cursed" (Yeshayah 65:20).

A child's lapses do not count as sin because he lacks full da'as. By the same principle, certain shortcomings of a great person are not counted as "sin" at all relative to his lofty level. The Sefas Emes notes that the verse about the future even speaks of "the sinner at a hundred years," showing that sin is always measured relative to one's standing and era.

וגם במלאכים מצינו חטאים כי אין שיעור לזה וז"ש בת ק' כבת כ' לחטא שהיתה נקוי' מחטא כנ"ל:

And even among the angels we find "sins," for there is no fixed measure to this; and this is the meaning of "at a hundred she was like twenty regarding sin" — that she was cleansed of sin, as above.

Even angels are described as capable of "sin" relative to their exalted level, proving that "sin" is a relative, not absolute, standard. So Rashi means that Sarah at one hundred stood on the elevated rung where, like the angels — or like a child below the age of accountability — she was reckoned wholly cleansed of sin at her own lofty measure.

Summary: Since no human is literally without sin, Rashi's praise that Sarah at a hundred was "like twenty regarding sin" must mean she stood on a level where her shortcomings were not reckoned as sin at all. Just as a child below the age of accountability lacks the da'as to be charged with sin, and just as even angels can be said to "sin" relative to their lofty rung, sin is always relative to one's level — and Sarah had risen so high that she was truly cleansed of sin.