John Gill Commentary Deuteronomy 15:13

"And when thou lettest him go free from thee, thou shalt not let him go empty:" — Deuteronomy 15:13 (ASV)

And when you send him out free from you
When he discharged him from his servitude, and made him a free man:

you shall not let him go away empty ;
without anything to support himself, or to put himself in a way of business; since he worked entirely for his master during his servitude and therefore could not have earned or saved anything for himself.