If one follows Shinobu ORIKUCHI's theory, originally amatsu tsumi was written as 雨障, implied how during the rainy season, farmers stayed indoors and were repentant of their misdeeds.
折口信夫は、天つ罪は元は「雨障（あまつつみ）」で、梅雨の時期に農民が忌み蘢ることを指していたという説を唱えている。