וַיֹּ֤אמֶר יְהוָה֙ אֶל־מֹשֶׁ֣ה וְאַהֲרֹ֔ן זֹ֖את חֻקַּ֣ת הַפָּ֑סַח כָּל־בֶּן־נֵכָ֖ר לֹא־יֹ֥אכַל בּֽוֹ׃
And the LORD said unto Moses and Aaron: ‘This is the ordinance of the passover: there shall no alien eat thereof;
Read kabbalistic (mystical) interpretation of Exodus 12:43: and classical mystical sources.