Parshat Bo describes the climax of the plagues on Egypt, culminating in the first Passover, and concluding with the laws for the practice of Passover for all generations:
I note the following passage:
43 The Lord said to Moses and Aaron: This is the law of the passover offering: No foreigner shall eat of it. 44 But any slave a man has bought may eat of it once he has been circumcised. 45 No bound or hired (gentile) laborer shall eat of it. 46 It shall be eaten in one house: you shall not take any of the flesh outside the house; nor shall you break a bone of it. 47 The whole community of Israel shall offer it. 48 If a stranger who dwells with you would offer the passover to the Lord, all his males must be circumcised; then he shall be admitted to offer it; he shall then be as a citizen of the country. But no uncircumcised person may eat of it. 49 There shall be one law for the citizen and for the stranger who dwells among you.A circumcised slave is considered part of the community of Israel, while a free gentile cannot be. In order to become part of the community, a gentile must take a stand on his very flesh to be recognized. Once he does so, however, the same duties and privileges will apply to him. Note that slavery in this context is NOT the same kind of slavery that the Hebrews experienced in Egypt. As is discussed later in Exodus, a person who buys a slave is strictly bound by rules about how to take care of him/her, and in the year of the Jubilee (every 50 years) all slaves are released. We see here, that even as the Hebrews are liberated from slavery, they are reminded about the intrinsic humanity of slaves -- a slave who is taken in and circumcised is part of the community, subject to the same laws and welcome to participate in the rituals.