Comentario sobre Exodo 12:44

ומלתה אתו אז יאכל בו WHEN THOU HAST CIRCUMCISED HIM THEN SHALL HE EAT THEREOF — “he” means his (the slave’s) master; this tells us that the neglect to circumcise his slaves bars him from eating of the Paschal offering. This is the opinion of R. Joshua. Rabbi Eliezer, however, said: the neglect to circumcise his slaves does not bar him from eating of the Paschal offering. The objection was raised: if this be so what means “Then shall he eat thereof”? — The reply was given: “He” means the slave, not the master (the meaning being that the slave, so long as he is uncircumcised may not eat of it) (cf. Mekhilta d'Rabbi Yishmael 12:44:2).

But every slave: The circumcision of slaves is an obligation on the master, from Abraham (Genesis 17:12) and onward. We are also commanded about the rest of slaves on Shabbat and holidays. And all of this raises the status of the slave, that it be slightly less than his master. And therefore when he is circumcised, he immediately eats from the Passover sacrifice like his master. But at the end of the Second Temple [period], when character traits became corrupted through the kings of the House of Herod and Israel learned the ways of the gentiles and the kings and ministers and wealthy ones particularly loved to copy the Romans - and we know that the Romans were cruel to their slaves - there were Israelite masters that did not want to circumcise their slaves in order that [the slaves] should not think of themselves as Israelites or [even] as people. The Sages of Israel then arose and decreed that whoever would not circumcise his slaves would not eat from the Passover sacrifice. And in my opinion, their intention was that one who does not consider his slaves to be like people is not fit to be among those that celebrate the festival of freedom. This is the position of most of the Sages, and it is taught anonymously in the Mekhilta (and according to Rashi's textual variant, it is the opinion of R. Yehoshua; and according to Tosafot's variant, it is the opinion of R. Akiva). But R. Eliezer says, "The circumcision of his slave does not impinge upon his eating from the Passover sacrifice"... As he did not want anything that was not in the Torah or in the tradition to be innovated, and he never said anything that he did not hear from the mouth of his teacher. But the rest of the Sages of Israel would innovate ordinances according to the needs of the times. And they had to excommunicate R. Eliezer, as he would protest against everything that veered from that which was passed on to him from his teachers. 

ועצם לא תשברו בו, ”you are not to break a bone of it.” Seeing that the Passover lamb is to be eaten על השובע, as the final part of the meal, so that it satiates the person consuming part of it, breaking bones of it would create the impression in the viewer that the person doing it was left hungry after eating its meat. Alternately, the meaning could be that on that occasion, when the meal was being consumed hurriedly, while standing up, the Israelites would try and stuff themselves as much as they could in anticipation of a long march. Such behaviour would contradict the festive nature of the meal.