And you shall be holy to Me, for I, the Lord, am holy, and I have distinguished you from the peoples, to be Mine. (Vayikra 20:26)
So I said to you, You shall inherit their land, and I shall give it to you to possess it a land flowing with milk and honey. I am the Lord your G-d, Who has separated you from the peoples. (Vayikra 20:24)
Blessed are You, Hashem our G-d, King of the universe, Who separates between holy and secular, between light and darkness, between Israel and the nations, between the seventh day and the six days of labor. Blessed are You, Hashem, who separates between the holy and the secular. (from the Havdallah)
For You set them apart from among all the peoples of the earth, Your inheritance, as You spoke through Moses Your servant, when You brought our fathers out of Egypt, O L-rd, G-d. (I Kings 8:53)
For something to reach the level of kedushah and be sanctified to Hashem it must be separated from that which is impure.
Rabbi Kahane z"l wrote in Or HaRa'ayon
"G-d decreed upon holy Israel that they must be separated from impurity and from the impure nations. The idolatry and the foreign culture of the nations cannot coexist with G-d's Torah or with G-d himself."
Separation is the key to our redemption. Hashem has brought us out of the nations back to our own land but we are still mingling with the nations. We must separate ourselves from that which is unholy spiritually, mentally and physically. We must begin separating from the non-Jews, Yishmael and Esav and from the Erev Rav among our own people.