Albert Barnes Commentary Deuteronomy 15:15-18

"And thou shalt remember that thou wast a bondman in the land of Egypt, and Jehovah thy God redeemed thee: therefore I command thee this thing to-day. And it shall be, if he say unto thee, I will not go out from thee; because he loveth thee and thy house, because he is well with thee; then thou shalt take an awl, and thrust it through his ear unto the door, and he shall be thy servant for ever. And also unto thy maid-servant thou shalt do likewise. It shall not seem hard unto thee, when thou lettest him go free from thee; for to the double of the hire of a hireling hath he served thee six years: and Jehovah thy God will bless thee in all that thou doest." — Deuteronomy 15:15-18 (ASV)

The commands here are repeated from Exodus 21:2-6, with amplifications relative to the maidservant (Deuteronomy 15:12) and to the making (Deuteronomy 15:13 and following) of generous provision for launching the freed servant on an independent course of life. The release of the servant is connected with the sabbatical principle, though not with the sabbatical year. It is also noteworthy that the prospect of a gift of this sort, the amount of which was left to the master’s discretion, would be likely to encourage diligence and faithfulness during the years of servitude.

He hath been worth a double hired servant to thee, in serving thee six years (Deuteronomy 15:18) – “that is,” such a servant has earned twice as much as a common hired laborer would have done in the same time.