The Bible teaches us we are justified by faith alone (Rom.5:1).
Meaning... our approval with God is not on the basis of our own works but faith in the righteousness of Christ.
Which is possible because "He made Him who knew no sin to be sin on our behalf, so that we might become the righteousness of God in Him" (2 Cor.5:17).
It's this truth that assures believers of everlasting life.
But it also does something else:
It frees us up to do the kingdom work God has called us to do.
We don't need to obsess over guilt, regret and whether we're saved...
... because He's accepted and liberated us to contend for Him every day He gives us breath.
For there is no condemnation for those who are in Christ Jesus (Rom.8:1)!
So... we can quit being introspective about our failures and get on with doing good for His glory.