Question

But he who dares not grasp the thorn should never crave the rose meaning

Answer 1

This means that courages peole can only succeed as who is scared cant take courageous steps and
fail in life....

Answer 2

Here the rose relates to a high positions with many features and the thorn relates to the hardships, responsibilities and the difficulties that come along with it.
So the quote states that if one is not willing or ready enough to accept and face the problems, responsibilities and hardships, should not ask for / crave those high positions.