Reference for Keritot 49:53

אלא ש"מ נדבה היא

but sin-offerings and guilt-offerings only as obligatory sacrifices; and the reason why one brings at all a suspensive sin-offering, although the sin is uncertain, is to afford him protection, because the Torah has compassion upon the lives of Israel.<span class="x" onmousemove="('comment',' Viz., to spare the trespasser punishment.');">³⁴</span>

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