In the OT, sanctify = legally/externally purify so that the unclean can perform the cerimonies/rites. It was the standard by which you could determine whether or not you could perform such cerimonies/rites.
The OT sanctification rites were merely external. Their purpose was to teach man about his sin and the burder of his sin, as well as symbolize what the Messiah would do later, which was real forgiveness of and purification from sin.