The concept of definitive sanctification is distinct from the false notion of sinless perfection this side of heaven, because the other complementary way in which we should speak of sanctification is in terms of “progressive sanctification”. The very word “progressive” implies that there is progress to make in our holiness.
“For this is the will of God, your sanctification,” (1 Th 4:3) St. Paul writes to a group of mostly non-Jewish Christians in Thessalonica who had formerly worshiped idols and casually participated in a culture steeped in sexual promiscuity. Sanctus is the Latin word for “holy”. The English word “sanctification” uses the verbal form “sanctify”, adding the suffix “-ation”. So, sanctification refers to “being made holy”. Because God is holy, people God brings into relationship with himself must be made holy. If they are to dwell with them, they must be holy, or else destroyed. But what does it mean to be holy, and how are we as creatures made holy?
To be holy means to be set apart, separated from anything that is either profane or merely common. God is holy in an absolute sense, because he is the Creator and everything else is his creation. He is above and beyond all that he has made. We especially think of him as holy, however, in the sense of moral perfection. Reasoning creatures such as angels and humans have become evil and wicked. Even the animal creation sometimes evidences such disorder and confusion — though arguably never the degree of perverse cruelty that humanity has perpetrated on itself through gas chambers, serial murders, abuse, and torture — that we would not have expected to see in the Garden of Eden apart from the serpent who appears as a devious intruder. We would not expect to see, for example, a mother abandon or murder her child, but sadly, such things happen in a cruel world that has forgotten its creator and his wise design for it. God is holy because he is entirely righteous and separate from evil.