"What good is it, my brothers, if someone says he has faith but does not have works? Can that faith save him?"
James 2: 14
"You see that a person is justified by works and not be faith alone."
James 2: 24
It is very important that we know that we have a faith that truly saves us! Satan has always acted to deceive people by his lies. Paul is so clear when he tells us in Ephesians 2: 8 "For it is by grace you have been saved, through faith.". However if the faith we have is true saving faith, it will effect the way we live for good for Paul also says in Romans 6: 2 "We died to sin; how can we live in it any longer.". So if our lives have not been changed by the faith we have, then it is not real faith which comes from God, and so is a dead faith.
Paul goes on in the 6th chapter of Romans and tells us that if we have true saving faith we are united to Christ in his death and resurrection, so that we have died to our old life and been raised with Christ to a new life which is created to be like God in true righteousness and holiness (Ephesians 4: 24). This means that true faith which saves from death and hell is revealed in the way we live our lives in our faith.
If our lives do not show this divine life then our claim to be saved is a lie, this is why James tells us that a person is justified by works and not by faith alone.
If we look at the teaching of Jesus in what is know as the Beatitudes (Matthew 5: 3-12) we see that if we have a true faith we will be merciful to others like the mercy we have received from God. Also a true faith hungers and thirst for righteousness, which is acting in the likeness of Christ. Then Jesus in the Lord's Prayer tells us that true faith reveals a forgiving spirit like the forgiving of Jesus that saves us.
This life which is brought about by grace through faith is marked by love, which is like the love which we have experienced from Jesus.
The great question every believer needs to ask themselves is whether the way we live shows that our faith in Jesus has truly changed our attitudes in our relations to other people.