John Gill Commentary Exodus 12:44

"but every man`s servant that is bought for money, when thou hast circumcised him, then shall he eat thereof." — Exodus 12:44 (ASV)

But every man's servant that is bought for money And so his own property:

when you have circumcised him ; as such an one ought to be, according to the covenant of circumcision given to Abraham, (Genesis 17:13Genesis 17:27) , though one should think not without his consent;

Therefore care was to be taken to purchase such servants as would be willing to conform to that rite, and pains were to be taken with them to instruct them in it, and persuade them to it; to which, when they had submitted, they had a right to eat the passover, but if they did not, it was not allowed:

then shall he eat thereof ; but not otherwise.