Even though the soul and the spirit are connected, they are separable
The Bible says in Hebrew 4:12 NLT:
“For the word of God is alive and powerful. It is sharper than the sharpest two-edged sword, cutting between soul and spirit, between joint and marrow.”
And in 1. Thessalonians 5:23 NLT, it says:
“Now may the God of peace make you holy in every way, and may your whole spirit and soul and body be kept blameless until our Lord Jesus Christ comes again.”
These passages make it very clear, that there is a distinction between the soul and the spirit.
Humans are spirit beings, who live in a body and possess a soul. The real person inside of us is our spirit. Our soul consists of our mind, will, and emotions. Our bodies are what we live in, while we are here on earth.
When Jesus Christ chooses us to become His follower, our spirit is instantly reborn and made new, as stated in 2. Corinthians 5:17:
“This means that anyone who belongs to Christ has become a new person. The old life is gone; a new life has begun!”
On the other hand, our soul is not born again, but instead needs to be transformed by the renewing of our minds, as it says in Romans 12:2 NLT:
“Don’t copy the behavior and customs of this world, but let God transform you into a new person by changing the way you think. Then you will learn to know God’s will for you, which is good and pleasing and perfect.”
This is why so many believers can continue to struggle with sin even after accepting Jesus Christ. Their soul still needs be purified and washed clean!
“Since you have purified your souls in obeying the truth through the Spirit in sincere love of the brethren, love one another fervently with a pure heart, having been born again, not of corruptible seed but incorruptible, through the word of God which lives and abides forever!” 1. Peter 1:22-23 NKJV
Demonic spirits can also remain in our souls, and must be driven out, as Jesus commanded to do, when He said:
“These miraculous signs will accompany those who believe: They will cast out demons in My name!” Mark 16:17 NLT
Many find it very hard to believe, that a born-again Christian can have a demonic spirit. It is because they simply don't understand the difference between the soul and the spirit of a person. They believe everything is made new the moment a person accepts Jesus.
But, it is through the soul, that demonic spirits torments and possesses people! Like the woman that Jesus delivered, whom an evil spirit had crippled for eighteen years, causing her to bend double so she was unable to stand up straight. (See Luke 13:11)
Or, like the boy, who suffered from terrible seizures that caused him to oftentimes fall into fire or water. Jesus rebuked the demon in the boy, and it left him. In that very moment, the boy was well! (See Matthew 17:15, 17)
I pray that the God of peace make you holy in every way, and may your whole spirit and soul and body be kept blameless until our Lord Jesus Christ comes again! God will make this happen, for He, who calls you, is faithful! (See 1. Thessalonians 5:23-24)