Catholics believe we are saved by the actions of Christ on the Cross and our original sin washed away through baptism. We have the faith in Christ that He has already saved us through His works.
“Faith alone” while a protestant belief is not very different than the Catholic understanding. While we are saved by our “faith” in Christ, or better put, we know that Christ died on the cross for our salvation, this is by no means complete. We do posses faith in the Love and Mercy of Christ but this faith is further reinforced by the “works” Christ performed and ultimately His sacrafice on the Cross, to say nbothing of His continued works. Faith and works hand in hand have led to our belief in our salvation.
Many non-believers continually ask for proof, even us who believe continually need our spirits and faith recharged by tangible evidence. This is human nature. While the apostles did have rock solid faith that Jesus was indeed the Son of God, the works He performed furthered that faith and His ultimate work, His sacrafice on the cross and ressurection demonstrated that faith in salvation fully.
We as Christians spread the news of salvation through our own faith and works as well. Faith by itself naturally comes with works for it is the natural progression and compliment of works. We are asked by Christ to “love others as I have loved you”. We have faith that our parents love us by that faith is reinforced by works and actions that our parents perform. Our belief in salvation is reinforced by our faith, which is justified by works, which are in turn justified again by faith. If we did not need faith and works to know we are saved, then Christ need not have died on the cross.