This is an important question Louise.  Allow me to attempt an answer on that issue.
 
We need to understand what salvation is in order to grasp the essence of this issue.  Salvation comes from God.  I am not able to save myself, nor can I save you.  We need something (someone) outside of ourselves. That is where God comes in.  In becoming a perfect man, he bore the punishment on sin for all those who believe.  The work is His, not ours.  The proof that Christ’s sacrifice was accepted is his resurrection from the dead.  He did it all.  All we do is believe.
 
John chapter 10 verse 28 says: “I give them eternal life, and they shall never perish; no one can snatch them out of my hand”.
 
That is a clear statement.  More importantly, salvation is a gift that we receive by faith, not by works.  There are no other conditions.  You see, if I can “remain” saved because I remain "faithful", then, salvation comes from Jesus and myself.  For one thing, that degrades His work.  And we still have a problem.  I don't trust myself when it comes to Eternal Salvation.  I sort of need something "outside of me".  I really think it comes from above.  Those who think that they can keep their salvation by being "faithful" are spiritually "proud".  Not cool.  It also forgets that God the Spirit is with us... by the way...
 
In essence, once you have Eternal Life, it is impossible to lose it.  That’s part of the joy of salvation.  We can believe in the word of Christ and enjoy our salvation day by day.  By not being distracted with "that" issue (eternal salvation), we can focus on a more important element.  One that has the other as object.  
 
According to Scripture, once we believe, we are "sealed" with the Spirit.  That abides. It is not an uncertainty. It is not something that needs to be repeated, again and again.  We never see in the Bible being again sealed by the Spirit. It is not a partial or conditional blessing, or constantly in need of renewal, just as you need to eat every single day. Not the case with the sealing of the Holy Spirit. It is a gift given at new birth and it remains with us forever.
 
Ck this out: http://www.eternalsalvation.org/The%20Eternal%20Security%20of%20the%20Believer.h tml