When I speak of justification I do not assume an imputed state or standing before God. I assume a real, righteous, quality of a man's soul that results in the first instance from the infusion of grace merited by our Lord on the cross. This quality of the man's soul can increase after he is justified (became a child of God), making him even more justified. If this man who was once justified does good works for the love of God, God will reward them by justifying him further still (pouring more faith, hope and love into his soul).
So when I state that a person is justified by works, I do not mean that a man translates from the state of being a child of wrath to being a child of God, through good works. I mean that a person who is already justified (saved, a child of God) increases in justification.
Or as Trent puts it:
THE INCREASE OF THE JUSTIFICATION RECEIVED
Having, therefore, been thus justified and made the friends and domestics of God,[49] advancing from virtue to virtue,[50] they are renewed, as the Apostle says, day by day,[51] that is, mortifying the members[52] of their flesh, and presenting them as instruments of justice unto sanctification,[53] they, through the observance of the commandments of God and of the Church, faith cooperating with good works, increase in that justice received through the grace of Christ and are further justified, as it is written:
He that is just, let him be justified still;[54] and, Be not afraid to be justified even to death;[55] and again, Do you see that by works a man is justified, and not by faith only?[56]
This increase of justice holy Church asks for when she prays:
"Give unto us, O Lord, an increase of faith, hope and charity."[57]