Book of Melachim

Regarding the reason why the Jews sinned while living the Land of Holiness and later when in the impurity of exile repented when seemingly it should be the opposite.

1 - When the Jews were in Eretz Yisroel, Hashem showed them great love and they were able to attain high spiritual levels without much work. This led to a laxity since they believed they were already holding where they should be and did not strive to reach higher. However the evil inclination does not stop and is always trying to dig in and therefore he started getting them on little things which eventually led to worse and worse things. In exile they knew they had to work hard and since they were always on guard, they did not give evil a chance to penetrate.

2 - Due to the great holiness of Eretz Yisroel even a minor act that was not done properly could be considered a big flaw. It is the way of one flaw to lead to second larger flaw and so on. This does not apply in exile and it was easier to guard against the first round of flaws since they were more tangible. In fact it works the opposite there where even a minor act of holiness since it is performed in a situation of such great impurity is considered very valuable and then leads to more good actions.