R’ Yonason Eibshitz give us an interesting insight into the breaking of the luchos. The luchos were written ‘Betzba Elokim’, the finger of the lord. Using the word Elokim brings out that the first luchos were written with midas hadin, the attribute of judgement. Moshe Rabbeinu knew that if he came down from Har Sinai with the luchos in tact, Klal Yisrael would do tshuva on the sin of the calf, after all it was only 3000 people who actually sinned. However the tshuva would be done because of fear of judgement. This would have set Klal Yisrael on a path of yirah, doing what is right because of fear, which in the long term is not the preferred way. Moshe Rabbeinu wanted to go with midos harachamim, the attribute of mercy, therefore he broke the luchos so he would have to write a new set and hakosh baruch hu would change from din to rachamim.