So then each of us will give an account of himself to God. — Romans 14:12
If you notice, that verse says “each of us.” That means believers and unbelievers alike. So, the question is, what if, as a believer, I have a poor account to give on that day? What we need to remember is that when we were saved by God, Christ covered our sins on the cross — past and future. But we also know that we still struggle daily against sins and thus need to continually look to the sacrifice Christ made for us (I John 1:9).
The thing to remember is that we are NOT saved by our works but by the blood of Christ. If we are pointing to a lifetime of good works as our salvation then we are relying on our own efforts and not Christ’s. And we will not enter into the Kingdom of God. Instead, our acceptance on that day will be on the basis of Christ’s atoning death.
What then, is the purpose of our deeds once we have been saved? The recounting of our deeds will be evidence that Christ died for us. For some there will be ample fruit, and for others there will be little to point to. Both, however, will enter based on the blood of Christ. Depending on what fruit was shown in our deeds, we will be rewarded accordingly in the kingdom to come.
For more on this, see John Piper’s recent Q&A at Desiring God.