Parshat Ki Tisa
Moshe is preparing to go up to Har Sinai for the second time to get the new set of tablets. Hashem tells him (in 34:1-4) that he has to hew two new stone tablets like the first set, etc. and Moshe hewed his own stones.
Why did Moshe have to do this? He did not have to hew his own stones the first time around - Hashem gave them to him. Why the second time did he have to bring his own?
Rashi says that Hashem said because you broke the set I gave you, you have to bring your own this time.
Sometimes you get something for your kid. Maybe a toy or a book or whatever. The kid breaks the toy. Happens in my house all the time. They actually prefer dismantling the toys and seeing how they are constructed rather than actually playing with them!
So you get your kid a toy and he breaks it fairly quickly. Are you going to run out and by him a new toy right away? Usually not. You will make the kid earn it. You want the child to learn responsibility and about waste. He has to learn the value of the item and thereby treat it better in the future.
So too by Moshe. You broke it, so bring your own this time. Moshe was being taught the real value of these tablets. true he broke the first set for a good reason and it was justified. But forcing him to hew his own stones and shlep them up the mountain really teaches Moshe the value and increases his level of respect for the tablets. In general he will treat them better and with more respect the next time.
When you invest your own efforts in something, you respect it that much more.