If we have put our faith in Jesus and are following Him, God wants us to know that we have been saved. We do not need to worry about that. It is not a case of whether or not we have done enough because our salvation does not depend on our works but on God's grace. Relax! God has made you His child and no one can take you out of His hand (John 10:28).
This is the doctrine of eternal security.
However, it does leave us with another question: Can you reject Jesus? No one else can take you out of His hand but, can you climb out?
How Can I Know That I Am A Christian?
Once Saved, Always Saved?
There is a school of thought that says that a Christian cannot lose his/her salvation even if he/she turns away from Jesus. For them, this is an important and non-negotiable principle.
But, is that what the Bible teaches?
Personally, I think there are many passages that teach that a person can lose his/her salvation. The counter view seems to be built on an over-inflated understanding of grace (i.e. God is so gracious he will save even the apostate). They explain passages about people falling away by saying "Well, they cannot have been real Christians in the first place".
I believe the Bible traches that it is not about starting the race, but finishing the race (Matthew 24:13).
But what do you see in the Bible?
Arguing that a Christian cannot lose his/her salvation
Is It True For Christians That "Once Saved, Always Saved"? - Dr Roger Barrier (CrossWalk)
Personal note: I find this article so weak that it persuades me of the opposite. Dr Barrier cites various passages about people falling away from Jesus but, somehow, concludes that it cannot happen. What do you think?
Eternal Security Or Faithful Faith? - Bobby Harrington (Renew.org)
Offers a good overview of the different positions. Argues that a person can lose his/her faith