When thou hast circumcised him; for the master had a power to circumcise such persons, Genesis 17:12. And though it is probable, that by their interest in them, and a diligent instruction of them, they made them willing to receive circumcision, yet it seems they had a power to compel them to it; but then circumcision was not to them a seal of God's covenant, nor of their religion, for that must be matter of choice, but only a civil badge, or a note of that family or people into which they were politically incorporated.
Related Commentaries of Exodus 12:44
Exodus 12:44
44 But every man's servant that is bought for money, when thou hast circumcised him, then shall he eat thereof.