Sforno on Exodus 18:22/ספורנו על שמות י״ח:כ״ב

1והקל מעליך, the many minor disputes which do not need to be adjudged by you, personally.

2ונשאו אתך, they will give you the chance to give your full attention to those problems that are complicated by sharing the burden of leadership with you. They will also dispense knowledge to the people.