However, the passage does not conclude that the believer is "adding nothing to faith" as you claim; it says the opposite, that man is freely collaborating with grace. These are relevant paragraphs also:
1993 Justification establishes cooperation between God's grace and man's freedom. On man's part it is expressed by the assent of faith to the Word of God, which invites him to conversion, and in the cooperation of charity with the prompting of the Holy Spirit who precedes and preserves his assent:[...]
2001 The preparation of man for the reception of grace is already a work of grace. This latter is needed to arouse and sustain our collaboration in justification through faith, and in sanctification through charity. God brings to completion in us what he has begun, "since he who completes his work by cooperating with our will began by working so that we might will it:"50
- Indeed we also work, but we are only collaborating with God who works, for his mercy has gone before us. It has gone before us so that we may be healed, and follows us so that once healed, we may be given life; it goes before us so that we may be called, and follows us so that we may be glorified; it goes before us so that we may live devoutly, and follows us so that we may always live with God: for without him we can do nothing.51
2002 God's free initiative demands man's free response, for God has created man in his image by conferring on him, along with freedom, the power to know him and love him. The soul only enters freely into the communion of love. God immediately touches and directly moves the heart of man. He has placed in man a longing for truth and goodness that only he can satisfy. The promises of "eternal life" respond, beyond all hope, to this desire:
- If at the end of your very good works . . ., you rested on the seventh day, it was to foretell by the voice of your book that at the end of our works, which are indeed "very good" since you have given them to us, we shall also rest in you on the sabbath of eternal life.52
(GRACE)
2011 The charity of Christ is the source in us of all our merits before God. Grace, by uniting us to Christ in active love, ensures the supernatural quality of our acts and consequently their merit before God and before men. The saints have always had a lively awareness that their merits were pure grace.
Thus, there can be no human works involved, since it is all of grace by your own definition. (Rom.4:4)
If it is all of grace than it must all of faith (4:16)
Human response is not considered a 'work' since it does not entail any human merit on the part of the responder, he is but yielding to grace (Rom.6)