Are you familier with the term "psyche" .. most people today ( irreligious intelectuals that is..) use this term in place of the christian concept of " soul" Unfortunately for them - it means literaly (in greek to english) "soul" . Anyway that was my intro.
It is impossible , so far as I have tried, to empirically prove the existance of soul, I think the soul is our element that is spiritual / part of the world unseen... For a True believer the soul is part of our body that is one with it, It is the part that will not be destroyed in us but rather continued on after death. The soul is eternal but still subject to God. We end up in heaven or hell.. not in the body we have now.. but our soul ends there... and . for christians I would say takes on a new body that perfectly portray's God's glory.
Perhaps these passages contrast the soul for an unbeliever with the soul of a believer who has been saved ... \...
James 1: 20" Therefore lay aside all filthiness and overflow of wickedness, and receive with meekness the implanted word, which is able to save your souls. "
Matthew10:28 "And do not fear those who kill the body but cannot kill the soul. But rather fear Him who is able to destroy both soul and body in hell." ( Our souls are in God's hands )
I also think that an unbelievers soul allthough Uncomplimented by the Holy Spirit, still knows what God's "will" and good order for man should be.. i.e. killing = wrong .. stealing = wrong... Things like that....
Vlad! - Perhaps this is something you cannot prove. I know I cannot prove it Its one of those things that has to exist for our concept of what the Bible tells us.. the specifics are only speculates if you will.. - its more of a faith thing I think -.
Another example of this "problem".... the Holy Spirit - other than the Bible telling you that as a Christian you have been given The Holy spirit.. you cannot "prove" it, you can feel His working.. and how He directs you.. but Yeah.. only you can .. noone else can prove it for you

Maybe for a believer the soul is complimented by the Holy Spirit...
Hebrews 10:15- 18 "But the Holy Spirit also witnesses to us; for after He had said before, "This is the covenant that I will make with them after those days, says the Lord: I will put My laws into their hearts, and in their minds I will write them," then He adds, "Their sins and their lawless deeds I will remember no more." Now where there is remission of these, there is no longer an offering for sin. "
Hebrews 4:11-16
"11 Let us therefore be diligent to enter that rest, lest anyone fall according to the same example of disobedience. 12 For the word of God is living and powerful, and sharper than any two-edged sword, piercing even to the division of soul and spirit, and of joints and marrow, and is a discerner of the thoughts and intents of the heart. 13 And there is no creature hidden from His sight, but all things are naked and open to the eyes of Him to whom we must give account. 14 Seeing then that we have a great High Priest who has passed through the heavens, Jesus the Son of God, let us hold fast our confession. 15 For we do not have a High Priest who cannot sympathize with our weaknesses, but was in all points tempted as we are, yet without sin. 16 Let us therefore come boldly to the throne of grace, that we may obtain mercy and find grace to help in time of need. "
1 Thessalonians 5:23-23
23 Now may the God of peace Himself sanctify you completely; and may your whole spirit, soul, and body be preserved blameless at the coming of our Lord Jesus Christ.
Anyway... thats all I can afford to spend on this subject... I have an exam that I should be preparing myself for..
My thoughts.. disjointed - but presenting some form of a point..