To sanctify something is to make it pure or holy. You might see a priest sanctify a church in your neighborhood — that means it’s holy.
Sanctify often has a religious connotation. If you get married, you might have a religious ceremony to sanctify your union. That means the marriage is viewed as legitimate according to your religion. Sanctify can also mean that something is made free from sin, like when the Pope sanctifies a person. Or you can use it for anything that’s made right or acceptable. Your mom’s support may sanctify the odd outfit you wore to the family reunion. Thanks, Mom!