Apologies for my ignorance. Most of my knowledge about Judaism is second-hand and my question doesn’t seem to be addressed in the wiki
As far as I know, in the current days post-Temple, the way for Jews to atone for any sin (not even sure if sin is the correct concept for Judaism) is to seek forgiveness, make amends and to try not to repeat sinful behaviors. Why wasn’t this sufficient in the time when the Temple existed? Why were sacrifices needed?