What does " but the reflection and resolution had obtained a firm and habitual control over it" mear

Hi. can anyone help me with the meaning of this sentence?
" his temper was naturally quick but reflection and resolution had obtained a firm and habitual control over it"
what does " but the reflection and resolution had obtained a firm and habitual control over it" mean?

In this context, "reflection" would mean he's thought about his temper and "resolution" would mean he's resolved (determined) to correct it.

Another way to say it:
"He had a naturally quick temper but after thinking about it, became determined to correct the problem by developing strong habits to control it."