They would not be a part of the people of God. Now, please try to understand as you hear this, that God is not some arbitrary tyrant that says you must do as I do or you will be cut off. Rather, God is saying He is holy. Goodness and purity reside within Him. Because His nature is holy, those who come unto Him must be holy.
Light dispels darkness.
You do not have light and darkness at the same time. God is light and dispels sin, that is, darkness. To come unto God and to be with God and to have fellowship with God and to walk with God and to be God's people, means that you become like God, you become holy. Then we read in Leviticus where God is speaking to His people. The people have all of these things that they must do in order to make themselves holy.