Shemot 19:5-6

Now therefore, if ye will obey My voice very carefully, and be shomer over My brit, then ye shall be a segullah (treasured possession) unto Me above all people; for kol ha'aretz is Mine; And ye shall be unto Me a mamlechet kohanim, and a goy kadosh. These are the words which thou shalt recount unto the Bnei Yisroel.