Two Types of Sins

The sins of the primal couple and of their son were different in nature. Adam and Eve sinned bein adam laMakom, between man and Creator, while Cain sinned bein adam l’havero, against his fellow man, and therefore Cain’s sin was in a sense more serious.

This same thought appears in Parashat Noaḥ.

Rashi, quoting Breishit Rabba, notes that the parasha  begins with the generation of the flood and ends with the generation which built the Tower of Babel. The latter generation rebelled against God, while the earlier one did not. Yet it is the earlier generation which received the more severe punishment. This is because the generation of the flood quarreled among themselves, while in the generation of the Tower of Babel there was love and friendship. 

It is noteworthy that the same distinction applied between the generation in which the First Temple was destroyed and that of the Second Temple. Our Sages tell us that the First Temple was destroyed because the Jews violated the three cardinal sins: idolatry, adultery and murder. The Second Temple, though the generation was observant of mitzvot, was destroyed because of needless hatred among the Jews. The first destruction lasted seventy years, while the second destruction has lasted more than 1945 years.

This may be because, as Malbim comments, sinning against God, and even rebellion against Him, is ultimately a personal matter. However, sins between man and fellow man destroy society itself.