Why do we need to confess our sins if they have already been forgiven (1 John 1:9)?

1 John 1:9 “If we confess our sins, he is faithful and just to forgive us our sins and to cleanse us from all unrighteousness.” When we read 1 John 1:9, there is a question that comes to mind straight away. If Jesus died on the cross, once and for all for our sins, then [ ]