Humans are corrupt beings. They are this way due to the fall from grace in the Garden of Eden by Adam and Eve. No human on their own can make themselves clean. How can filth clean filth? It is impossible for there will always be filth left behind when this is done.
That was why God created the blood sacrifice. For centuries, it was the blood of the lamb. Then God allowed His Son to come amongst humans. He lived without sin, but witnessed sin. Then it was the humans that called for His death, His sacrifice, and so He went to the cross and shed His pure and clean blood. This Blood is so powerful that it cleaned all the filth from those that called upon Him as their Savior.
This salvation makes people change. That which gave them pleasure before no longer does and so they turn from that which was their old live in the filth. Sometimes though they do get dirty, but they ask God for His forgiveness and blessing and He gives it.
But humans are corrupt beings. They are told within the Bible that they must abide with Jesus. Live in His word and His teachings, but most do not. Soon they find themselves returning to those sins and forgetting to ask Jesus for His cleansing. Therefore, they falter and fall, until one day they are merely paper Christians. Their month says they are but their actions say they are the sin they once were.
Jesus called these the “lukewarm” and He said he would spew them from His month for they are no longer one with Christ or God and no longer worthy to amongst the counted.
Can they fix this? Yes they can, but many are so blinded they do not realize that they have faltered and fallen away. There are those that cry from the wildness calling upon them to repent and return to Christ. Some may listen, but most do not.

Mark Chapter 7:20 And he said, That which cometh out of the man, that defileth the man. 21 For from within, out of the heart of men, proceed evil thoughts, adulteries, fornications, murders, 22 Thefts, covetousness, wickedness, deceit, lasciviousness, an evil eye, blasphemy, pride, foolishness: 23 All these evil things come from within, and defile the man.
John 15: 1 I am the true vine, and my Father is the husbandman. 2 Every branch in me that beareth not fruit he taketh away: and every branch that beareth fruit, he purgeth it, that it may bring forth more fruit. 3 Now ye are clean through the word which I have spoken unto you. 4 Abide in me, and I in you. As the branch cannot bear fruit of itself, except it abide in the vine; no more can ye, except ye abide in me. 5 I am the vine, ye are the branches: He that abideth in me, and I in him, the same bringeth forth much fruit: for without me ye can do nothing. 6 If a man abide not in me, he is cast forth as a branch, and is withered; and men gather them, and cast them into the fire, and they are burned. 7 If ye abide in me, and my words abide in you, ye shall ask what ye will, and it shall be done unto you. 8 Herein is my Father glorified, that ye bear much fruit; so shall ye be my disciples. 9 As the Father hath loved me, so have I loved you: continue ye in my love. 10 If ye keep my commandments, ye shall abide in my love; even as I have kept my Father’s commandments, and abide in his love. 11 These things have I spoken unto you, that my joy might remain in you, and that your joy might be full.
Revelation 3: 14 And unto the angel of the church of the Laodiceans write; These things saith the Amen, the faithful and true witness, the beginning of the creation of God; 15 I know thy works, that thou art neither cold nor hot: I would thou wert cold or hot. 16 So then because thou art lukewarm, and neither cold nor hot, I will spue thee out of my mouth. 17 Because thou sayest, I am rich, and increased with goods, and have need of nothing; and knowest not that thou art wretched, and miserable, and poor, and blind, and naked: 18 I counsel thee to buy of me gold tried in the fire, that thou mayest be rich; and white raiment, that thou mayest be clothed, and that the shame of thy nakedness do not appear; and anoint thine eyes with eyesalve, that thou mayest see. 19 As many as I love, I rebuke and chasten: be zealous therefore, and repent. 20 Behold, I stand at the door, and knock: if any man hear my voice, and open the door, I will come in to him, and will sup with him, and he with me. 21 To him that overcometh will I grant to sit with me in my throne, even as I also overcame, and am set down with my Father in his throne. 22 He that hath an ear, let him hear what the Spirit saith unto the churches.