If by "sanctify" the author means "make holy" then it's impossible. Only God can make a day holy....and he already did it.
Lev 23:2 Speak unto the children of Israel, and say unto them, Concerning the feasts of the LORD, which ye shall proclaim to be holy convocations, even these are my feasts.
Halloween, All Soul's Day or All Saint's Day are not one of the holy days God created and cannot be made holy by man.