I hesitated to answer the OSAS question but decided to reply because I found other replies lacking.
 
I believe the problem in understanding this subject lies in a lack of rightly dividing the word of truth 2Ti 2:15 .
 
 The spirit is saved and regenerated by believing and confessing with your mouth Our Lord and savior Jesus Christ. This cannot be lost. You cannot be un-reborn again. This is the grace of God to you and a free gift to all who will believe and receive a new life in Jesus.
 
Many confuse salvation of the soul with salvation of the spirit. You can lose your souls salvation by living a carnal life not changing much but letting your flesh rule you instead of the Holy Spirit. The salvation of the soul is worked out by each individual who applies the word of God to their daily life. Php 2:12  This is a very in depth study much too long to put in a single post.
 
Let me refer anyone interested in understanding the difference between spirit and soul salvation to the following links for a full explanation.
 
http://www.ffruits.org/firstfruits/soulvsspirit.aspx
http://www.ffruits.org/firstfruits/scripturesalvation.aspx
http://www.ffruits.org/firstfruits/salvationpastpresentfuture.aspx
http://www.ffruits.org/firstfruits/salvationpastpresentandfuture.aspx
 
http://lampbroadcast.org/Books/SOS.pdf
 
May the links above clear up this subject.
Be blessed by this study,
 
Steve Shackleton