system
Given the following post, respond as if you're commenting on Reddit:
human
[DC] So uh... I hate to be insensitive, but why exactly was Batman so moved by the letter from (Flashpoint Paradox Spoiler)

His dad?

I mean, the actual content of the letter seemed... not at all evocative of emotion.

Was it just that it was a letter from his dad, to him?

Was it just that it was written by his dad?  Could it have read:

Milk
Eggs
Butter
Cheese

And still achieved a similar effect?
gpt
It wasn't just an old letter from his Dad that he wrote decades ago and someone found, it was a letter from his Dad who had lost his son and was older/ "present day" so it made it more meaningful to know they were recent thoughts. 

It was a sort of "goodbye" they never got to have and the whole circumstances involved to get that letter to him is why he tells Flash "You're one hell of a messenger."

The letter/Flash telling him his Dad was Batman made him realize how much like his father he was, since his death in that alternate timeline inspired his father to become the Batman, giving Bruce's choices more purpose and meaning.

His Father died when he was a young boy and now he has validation that his Father loved him, misses him and supports what he does, what's not to get emotional about?