When the racist white guy says to the slave, whose illiteracy he initially mocked, "I'm honored to have served with you. Honored."
"PAPA! Papa, don't go, I'll say anything!"
After Gabriel is killed and Benjamin doesn't know what to do with himself for a while, he goes to pack his son's things into his own bag. Benjamin then finds the flag Gabriel had been trying to repair from near the beginning of the film, and rides off to rejoin the others with said flag flying high. I'd say he'd found something more than revenge to fight for.
"Colonel! The line is faltering!" Hearing Jean who had never referred to Benjamin by his rank finally call him Colonel shows how much he has come to respect Benjamin.