לֹא־יִקְשֶׁ֣ה בְעֵינֶ֗ךָ בְּשַׁלֵּֽחֲךָ֙ אֹת֤וֹ חָפְשִׁי֙ מֵֽעִמָּ֔ךְ כִּ֗י מִשְׁנֶה֙ שְׂכַ֣ר שָׂכִ֔יר עֲבָֽדְךָ֖ שֵׁ֣שׁ שָׁנִ֑ים וּבֵֽרַכְךָ֙ יְהוָ֣ה אֱלֹהֶ֔יךָ בְּכֹ֖ל אֲשֶׁ֥ר תַּעֲשֶֽׂה׃ (פ)
Niechaj ci się to trudnem nie okaże, że go masz puścić wolno od siebie, gdyż podwójną płacę najemnika zasłużył u ciebie przez sześć lat; a pobłogosławi cię Wiekuisty, Bóg twój, we wszystkiem co przedsięweźmiesz.
Rashi
כי משנה שכר שכיר [IT SHALL NOT SEEM HARD UNTO THEE WHEN THOU LETTEST HIM GO FREE …] FOR [HE HATH BEEN WORTH] A DOUBLE HIRED SERVANT [UNTO THEE] — From here they (the Rabbis) derived the law that a Hebrew servant has to do service both by day and by night, and that is double as much as the labor of a man hired for day work only. And what is his service during the night? That his master gives him a Canaanite maid-servant with the object of raising children, and the children belong to the master (Sifrei Devarim 123:1; Kiddushin 15a).
Chizkuni
לא יקשה בעיניך, “it shall not appear an unreasonably hard rule to you;” (that you have to give him so much for “free”) The Torah reminds the owner that he had obtained far more value in labour from this “slave” than he would have had from an ordinary hired labourer working for him as he had been at his disposal not only during the daylight hours, etc. Our author suggests a different comparison, one found in Isaiah 16,14, according to which fixed labour is hired only for three years and this man has served six years. [Different calculations are made by different commentators; the basic common denominator agreed is that the Torah reminds the employer/owner, that this servant/slave has done more for him than a hired hand would have done. Ed.]
Da'at Zekenim
כי משנה שכר שכיר עבדך, “for he has worked for you twice as long as the wages that he received,“ a hired hand usually hires himself out for a period of three years. We know this from Isaiah 16,14: בשלש שנים כשני שכיר ונקלה כבוד מואב, “in three years, fixed like the years of a hired labourer, the glory of Moav shall shrink;” it follows that someone who has served his master for six years has actually served twice the length of a hired hand. The reason they hired such labourers for a period of three years was that if they had hired such a person for a term of a year or two years, sometimes the years are longer and sometimes they are shorter, depending it had more than one month of Adar. By making the term three years there could not be a dispute about how many days of labour this included.