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Assurance of Salvation is having full knowledge that you are 100% sure that you will go to heaven one day. It is knowing for sure that you are forever forgiven and eternally saved, even now and forever more.

This confidence is two fold:
 1.  Having been saved, a person receives a changed heart.  Not a change initiated by self, but one formed by God.  This change is proof that you have been saved.

"Therefore if any man be in Christ, he is a new creature: old things are passed away; behold, all things are become new." II Corinthians 5:17

Once the God-given change is received, the new saint is "in Christ". Those "in Christ" are the born again, saved. They have received the gift of God.

"For by grace are ye saved through faith; and that not of yourselves: it is the gift of God: not of works, lest any man should boast." Ephesians 2:8-9

The gift of God, which is eternal life (Romans 6:23), is eternally kept by God.
* He freely gives it.
* He freely keeps it.
* It lasts forever.
So once a person receives it (the proof of having received it is the changed heart) that person will have it forever. This is full assurance of salvation.

Assurance is not something acquired after salvation. It is something that a saved, born again person already has, but finally realizes he or she does indeed have it.

A person must only be sure they have received salvation. The changed heart is the proof. Did you get the change?

 2.  Once a person receives the changed heart, he or she begins to delve further into the things of God.  The Bible is the beginning of this adventure.  Once in the Bible, the promises of God are everywhere.  When the new Christian begins to place faith in these promises and sees God work through them, he or she has repeated confirmation that salvation has come and will stay forever.

Many have been saved and then begin to quit reading the Bible and forsake the assembling of themselves together for preaching and exhortation. Soon they forget how it all works and lose that initial joy. This is a backslidden condition. Salvation has not been lost, but fellowship with the Lord has. One only must come back to Jesus and repent of backsliding and He will take you back into fellowship. No need to attempt to be saved again, it was never lost, if you have received the changed heart to start-with.

Set of files on Assurance
Set of slides on Assurance
Set of slides on Salvation and Assurance - this starts with the new birth, salvation, and proceeds to assurance