Therefore we conclude that a man is justified by faith apart from the deeds of the law. (Romans 3: 28)

When we are saved, we are rescued from the penalty, the pain and the practice of sin. This rescue was performed through the death of Jesus on the cross of Calvary. It requires faith to believe that this has happened and that it has happened to us.

When we are justified, we are made right or regarded as right in the eyes of God. This too requires faith because who among us thinks that they are so perfect that they can stand blameless before God? Look at it this way. Suppose you owe money to a friend and could not repay it. But, another friend pays the debt for you. Now, even though you did not pay it, when your first friend looks at you, he does not see you as a debtor because you no longer owe him.

To say that we are justified by faith means we trust in the payment Jesus made to God on our behalf and believe that now God looks at us as ones who no longer owe Him for sin. The only way we could ever believe in such a justification would be by faith.