The Torah (VaYikra 36:35 and 43) tells us that the punishment of the tochacha was brought upon the Jewish people for their failure to observe the laws of shmitta. Rashi calculates that the 70 years of the exile between the first and second mikdash correspond to 70 shmitos and yovlos which were not observed. In his introduction to vol 1 of his tshuvos (#17-19), R’ Shmuel haLevi Wosner asks how is it that for hundreds of years while there were batei din of Nevi’im and Tzadikim the laws of shmitah were completely neglected?
R’ Wosner cites the Akeidah as explaining that the purpose of shmitah was not just for the farmer and his land to rest one year and devote that year to avodas Hashem, but that one year is the yotzei min haklal which is melamed al haklal – the one year is the reminder that the purpose of work during the other 6 years should not be dedicated to wealth for its own sake, but to providing one's needs for avodas Hashem. The Jewish people may have observed the letter of the law of shmitah, but they failed to properly absorb its attitude. "Lo shavsa b’shabsoseichem’, even amidst shabsoseichem, your superficial observance of shabbos, there was no real shabbos in attitude.
Nora v'ayom! - the entire tochacha punishment and all the sorrow of that parsha is not due to lack of observance, but due to a lack of appreciation of the attitude and values that observance is meant to imbue in a Jew. With all the talk around the 'net by some about the importance of -proxy over belief and the stress of conformity to halacha over faith, something to think about.