This has nothing to do with moral purity but being set apart for the work of redemption. That cannot mean that he made himself morally pure. Actually the words holy and sanctify are not the most difficult words to define. They mean nothing belongs to God anymore. He is not acknowledged.
Man is the center of everything.
The word holy then is the exact opposite of profane . Of or relating to religious objects, rites, or practices. The word holy can easily be understood as either referring to a thing or a person. It can mean either moral purity or setting apart for religious purposes. Here is the dictionary definition.