Sforno on Deuteronomy 16:15/ספורנו על דברים ט״ז:ט״ו

1כי יברכך, so that you will have a great deal of gathering in to do, and as a result, the poor will also find much to collect.

2והיית אך שמח, you will be completely joyful; no sadness will intrude on your happy frame of mind.