Charles Ellicott Commentary Exodus 12:43

"And Jehovah said unto Moses and Aaron, This is the ordinance of the passover: there shall no foreigner eat thereof;" — Exodus 12:43 (ASV)

No stranger. — Compare Exodus 12:48 for limitations. If a stranger wished to join, and would accept circumcision for himself and the males of his family, he might partake in the rite.