God...an indian giver???

This post is derived from a conversation I had with a friend the other night. One of the "hot" topics came up...Assurance of Salvation. The reason I'm writing this is I need your help. I am not necessarily the best at quoting scripture, but I remember what the verses mean.

The only way we can get to heaven is to accept that God loved us so much that He sent His only son to die for our sins. Grace. That's how we get to heaven. It's not earned by what we do. In fact, it's given to us. We didn't have to do anything to receive it exceipt acknowledge God as Lord of your life. Ok, so if the salvation was a gift given to us out of love, why would God take it away? The parable about the prodigal son is a story that comes to mind. It's an illustration about how a son strays from his father, doing everything rebellious, but then when he returns, the father has a celebration. The father wasn't mad, just glad his son was home. This doesn't mean the father wasn't hurt or sad while the son was gone...it's just that the father never disowned his son.

Now for the help...anyone have any verses to share regarding this issue??? Thank you in advance!