What the Bible says about Holy as Clean
(From Forerunner Commentary)
Here the word holy means "pure," "clean." This verse is repeated verbatim in I Peter 1:15-16, an application that cannot be denied, especially when connected to the subject, priesthood, of I Peter 2. Priests must be pure in the conduct of their lives because God is pure. We must be pure to be acceptable to Him, for it was immorality that defiled us in the first place. We must be pure to offer acceptable sacrifices to Him.
God begins the process by cleansing us by the blood of Jesus Christ, but He expects us to continue it through the keeping of His Word. We are purified through the keeping of His Word in the power of His Spirit (see, for instance, Ephesians 5:26-27). This requires the sacrifice of our lives in every aspect of life, and the whole aim is to produce the fruit of God—love.
John W. Ritenbaugh
New Covenant Priesthood (Part One)