first of all, even if he didn't do anything or other things not related to being a knight, the 'today' would keep returning eternally to the same day no matter what. He would go insane either way so it's better to use it, instead of just enduring it.
Second of all, he has this power because he wants to be a knight. If he didn't want to, he would never come to get this 'power' in first place.
It's so obvious on the manhwa that i wonder if you read it correctly.

If you have this kind of power why would you even want to be warrior and keep fighting/Dying especially when you don’t even have the talent of a swordsman??!
This doesn’t make sense let just be realistic, he could have given other ways of life a chance and he would have been successful, rather than sticking to dying like a fools who’s high on death!!
Just the amount of death he went through is insane that it can traumatise a person, if he had only 3 chances of resurrection would he still be stubborn and obsessed about being a warrior?
Sign what worthless resurrections, he doesn’t value life.