The Bible tells us we can be sure of our salvation.
1 John 5:13 King James Version (KJV)
13 These things have I written unto you that believe on the name of the Son of God; that ye may know that ye have eternal life, and that ye may believe on the name of the Son of God.
Wow...we are studying 1 John 5 this very day on the Jerusalem Thread. :-)
(Coincidence?)
The Greek behind this further reinforces the message. God is not one to give salvation and then take it away.
As simple and sure as this...
Acts 16:31 Douay-Rheims 1899 American Edition (DRA)
31 But they said: Believe in the Lord Jesus, and thou shalt be saved, and thy house.
Romans 10:9-10 Douay-Rheims 1899 American Edition (DRA)
9 For if thou confess with thy mouth the Lord Jesus, and believe in thy heart that God hath raised him up from the dead, thou shalt be saved.
10 For, with the heart, we believe unto justice; but, with the mouth, confession is made unto salvation.