Man is made of body, soul and spirit. Man was born in sin and so his spirit was dead at birth. Man is made in the image of God but his spirit is dead due to sin. Now he has a form of godliness but his spirit is dead. Man needs to be born again in the spirit to be made new. This is the reason Jesus came. Through His death and resurrection He was able to impart His Spirit into man. When His Spirit is received he becomes a new creation in Christ. This is called the born-again experience. Man now lives forever in his spirit. However the body and the soul are still not redeemed. The body and soul are still subject to man. God resides in his spirit but only those who walk according to the Spirit can subdue the body and soul.
The flesh which is a term for body and soul needs to be sanctified. Sanctification is a life-long process. To be fully sanctified is to be like Jesus. His Spirit in us does the work of sanctification as we submit to Him daily. Many don’t understand this process and so remain infants in their spirit. To grow in the spirit one needs to be filled with the Spirit and walk according to the Spirit. The Holy Spirit lives in us and He leads and guides us. He is our Helper, Comforter and Teacher. He is always communicating with us. He gives us His thoughts and feelings. All we need to do is listen to Him. When we acknowledge Him as Lord, He takes over. This is a daily surrender to His will. Remember, we are in a battle.
The battle for our soul is called spiritual warfare. The devil and the world conspire to distract us from our submission to the Lord. God is on our side but He has given us a free will to choose whom we will serve. Jesus had many following Him but only a few stuck with Him. So also today many are happy to be saved but few want to be His disciples. Many start well but then fall away due to the pressures of the world and the devil. We see this in every area of life. The battle can get fierce and some have lost their lives in following Jesus. We must surrender all to Him daily till we are called home to Him. There is no better life to live than in total surrender to Him.