Well, he prefaces it with "I think you are kind to the point of softness, magnanimous, unselfish, ready to share your last farthing; you have no envy nor hatred; you are simple-hearted, you pity men and beasts; you are trustful, without spite or guile, and do not remember evil.... You have a gift from above such as other people have not: you have talent."

Sounds like his brother probably satisfies at least 1, 2, and 3. That's why I say gentle; he says "you're a great guy, you have natural talent and the potential to be cultured, just need to work on your attitude and develop your talent".