וִהְיִ֤יתֶם לִי֙ קְדֹשִׁ֔ים כִּ֥י קָד֖וֹשׁ אֲנִ֣י יְהוָ֑ה וָאַבְדִּ֥ל אֶתְכֶ֛ם מִן־הָֽעַמִּ֖ים לִהְי֥וֹת לִֽי׃
And ye shall be holy unto Me; for I the LORD am holy, and have set you apart from the peoples, that ye should be Mine.
Read kabbalistic (mystical) interpretation of Leviticus 20:26: and classical mystical sources.