And whereas the Apostle saith, that man is justified by faith and freely, those words are to be understood in that sense which the perpetual consent of the Catholic Church hath held and expressed; to wit, that we are therefore said to be justified by faith, because faith is the beginning of human salvation, the foundation, and the root of all Justification; without which it is impossible to please God, and to come unto the fellowship of His sons: but we are therefore said to be justified freely, because that none of those things which precede justification-whether faith or works-merit the grace itself of justification. For, if it be a grace, it is not now by works, otherwise, as the same Apostle says, grace is no more grace. [Council of Trent, Decree on Justification, §8]
As faith is the "beginning of human salvation,…and the root of all Justification," it is entirely appropriate then for the Catholic to say that we are justified by faith. It's important, however, for the sake of clarity and understanding that it be made clear that it is a beginning; having been baptized, we then must, as the Apostle says, "with fear and trembling work out your salvation. For it is God who worketh in you, both to will and to accomplish, according to his good will" (Philippians 2:12-13), because faith without works is dead.