Justification is the legal declaration by God upon the sinner, where God declares the sinner to be righteous.
This declaration is based completely and totally on the work of Christ on the Cross.
A person is justified by faith that is, we are made right before God by his faith in Christ (excluding cults that teach a false Jesus). So this genuine faith in the genuine Jesus.
Romans 5:1
Therefore, having been justified by faith, we have peace with God through our Lord Jesus Christ,
We are not saved by our works or our works added to the sacrifice of Christ.
Our works, our good deeds, have absolutely no affect upon our salvation. Our good works do not get us salvation, nor do they help us keep our salvation.
This is because our good works are filthy rags before God
Isaiah 64:6
But we are all like an unclean thing,
And all our righteousnesses are like filthy rags;
We all fade as a leaf,
And our iniquities, like the wind,
Have taken us away.
If we could be saved by works, then righteousness would have been based on the law and Christ would not have needed to die.
"I do not nullify the grace of God; for if righteousness comes through the Law, then Christ died needlessly." But, Christ did need to die which proves our works cannot save us.
Galatians 2:21
I do not set aside the grace of God; for if righteousness comes through the law, then Christ died in vain.”
once saved, the person is now changed. He is a new creation and the old things have passed away.
This means that our old sinful ways are gone (or on their way out as we struggle against them).
It also means that we then do good works to honor God.
We don't do good works to be saved or stay saved. We do good works because we are saved.
I heard it said that you are not saved by good works, but you aren't saved without them. This means that our good works don't save us in any way, but once we are saved we naturally obey God's law and do good works which is a sign of our being saved.