Thank you for the interpretative question, “What is a clean spirit in the Bible?”
In thinking about how to answer the question, I like to suggest two approaches to a “clean spirit.”
A. The correlation between “evil spirit and “clean” spirit as being angelic beings.
In the Gospel, the term, evil spirit, refers to demons. For example, Mark 1 says this, “22 The people were amazed at his teaching, because he taught them as one who had authority, not as the teachers of the law. 23 Just then a man in their synagogue who was possessed by an impure spirit cried out, 24 “What do you want with us, Jesus of Nazareth? Have you come to destroy us? I know who you are—the Holy One of God!” 25 “Be quiet!” said Jesus sternly. “Come out of him!” 26 The impure spirit shook the man violently and came out of him with a shriek” {(NIV). (Citations are in the NIV).
The evil spirit or demon came out of the man. The question becomes can a “clean spirit” or an angel possess a person. As far as I know, I am not aware that an angel of God possesses a person.
Hebrew 1 says that angels are ministering spirits. The angels of God who didn’t rebel do not possess believers. They may help believers in their spiritual journey to God or their walk with God. When Jesus was in the Garden praying, the angels were there to strengthen him (Luke 22:43).
B. The correlation between “evil” or sinful heart and a clean heart before God.
In Acts 9, Simon the Sorcerer comes to faith, but his heart is not right with God. Peter exhorts him to repent so that he becomes right before God.
The text says this, “18 When Simon saw that the Spirit was given at the laying on of the apostles’ hands, he offered them money 19 and said, “Give me also this ability so that everyone on whom I lay my hands may receive the Holy Spirit.” 20 Peter answered: “May your money perish with you, because you thought you could buy the gift of God with money! 21 You have no part or share in this ministry, because your heart is not right before God. 22 Repent of this wickedness and pray to the Lord in the hope that he may forgive you for having such a thought in your heart. 23 For I see that you are full of bitterness and captive to sin.”
The implication is that a believer may become bitter and captive to sin. His spirit is not right with the Lord. He is walking in sin. Conversely, a believer who walks in the Spirit has a clean conscience and heart. In that sense, one may use the term, an evil spirit or a clean spirit. When a believer confesses his or her sins (I John 1:9), then one would say that his/her spirit is right with the Lord. It implies a ‘clean” spirit with that person from sin (Ezek. 36:26).
Summary: The Bible does not specifically use the term, clean spirit, referring to an angel or to the person’s spirit.
-Kingston