What is the literal translation of "Lo Sirdeh bo be'Farech"?
Targum Onkelos, Ibn Ezra: Do not subjugate him with hard work.
Sifra: Don't ask the Eved Ivri to warm you some water for which you have no need or to dig around the vine until you return (without telling him when you intend to return
Having already said in Pasuk 39 "Lo Sa'avod bo Avodas Aved", why does the Torah repeat it here?
Rashi (citing the Sifra): The current Pasuk refers to making him perform unnecessary tasks in order to torment him. 1
Why does the Pasuk insert "ve'Yareisa me'Elokecha"?
Rashi: Because nobody knows what is in his mind, whether the work is needed or not, other than Hashem.
QUESTIONS ON RASHI
Rashi writes that only Hashem knows what is Avodas Parech - unneeded. We find (in Pasuk 53) that we must stop a Nochri from making an Eved Ivri do such work! And what is Rashi's question (Pasuk 44), who will do such work for us?
Meshivas Nefesh: Perhaps there, "be'Farech" means hard work. However, Rashi did not say so!
Meshivas Nefesh #2: Avodas Parech includes what is unneeded, and work without a known limit 1
Refer to 25:43:1:2. The latter is known to people, and we need slaves to do such work for us. The Rambam (Hilchos Avadim 1:6) explains like this, but the Sifra and our text of Rashi implies that all of the tasks mentioned are not needed. The Pasuk implies that all Avodas Parech is not known to others, therefore it says "ve'Yareisa me'Elokecha"!
Rashi writes that Avodas Parech is unneeded. Why would a master do weaken his Eved Ivri by making him perform tasks that he does not need?
Toras Moshe: An Eved Ivri leaves at the end of six years, like Yetzi'as Mitzrayim. A master might think that he will not rejoice in this; sometimes he wants to remain a slave, "Ki Tov Lo Imach"; therefore, I will subject him to Avodas Parech, and he will be happy to go free! The Torah forbids this 'Chasidus'; it is folly.
The master can command matters that do not weaken him, just it is frustrating to toil for no need. Perhaps he wants to pain him! Alternatively, he orders him to do unneeded work, to prevent him from growing weak due to idleness, like Rava said about workers who carry burdens (Bava Metzi'a 77a). Rava said that they prefer working to being idle, i.e. they can say so to demand their full wage if the employer retracted, but if such an Eved Ivri says that he prefers to be idle, one cannot order him to do unneeded work. Or, they prefer doing needed work to being idle,(PF)