Sanctification means “to be set apart to God” and, necessarily then, “from evil.” It is positional—what God has done for us in the work of Christ (as in Heb. 10:10)—and practical—what we are responsible to do in view of that fact (as in Heb. 12:14). (The world holy has the same root).
The Spirit of God works on us with the purpose of setting us apart for God. When we accept the gospel of our salvation, we come into the realization that we no longer belong to ourselves, but to Him who died for us and rose again.
But now we are responsible in view of that to act accordingly, putting it into practice in every aspect of our life. A thing that is sanctified is holy (as in 2 Cor. 7:1).
R. Thonney (from the Y.P. Forum)