Part of the problem in understanding this lies in our view of holiness (i.e., separation, perfection). Unholiness is the absence of holiness. That may seem obvious, but I’ll unpack the statement.
To be succinct, “holiness” must exist for there to be “unholiness,” which is the absence of holiness. Therefore, “unholiness” can’t exist without “holiness.”
When God created the universe, everything was holy. God said it was “perfect/very good” in Genesis 1:31 (see also Deuteronomy 32:4). However, it would be a fallacy to assume that things would remain holy considering that man had the power of contrite choice, as did angels when they were created (i.e., man was permitted to “freely” eat).1
While God is holy and has an unchanging nature (Malachi 3:5), other created beings, including humans and angels (see Ezekiel 28:15), can fall from a holy state to an unholy state through sin—this is very similar to the confusion about whether something that is “perfect” can ever become imperfect. Of course, God is perfect and cannot become imperfect. But His creatures can, as Ezekiel 28:15 shows us. The misunderstanding comes from equivocating on the word “perfect.” Webster’s first definition for the word refers to something without fault or defect, which could apply to God or the original state of His creation. The third definition would only apply to God in that He is lacking in no essential detail and, as a result, cannot fall from perfection.
So, really the question should be: how can something unholy ever be restored to a perfectly holy state? It cannot be done of oneself. We need the help of the One who is perfectly holy. Only Jesus Christ, who is the perfect and holy God, can restore mankind to a holy state (2 Corinthians 5:21).