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Collect: Grant, O Gracious Lord, that I may always remain in thy favor, and if I fall that thou mayest bring me to life again by thy mercy, through Christ Our Lord. Amen.
In the Sed Contra, St. Thomas proves the thesis by an appeal to Ezekiel 18:24.
In the Respondeo, we must carefully distinguish the state of the question. Fr. Lagrange notes that "the problem is not whether a man who has already fallen can merit his own restoration; it is already established by article that he cannot, since fallen man cannot merit the first grace or justification. The meaning of the present article is: whether, at the time when a man is just, he can merit from God that, should he happen to fall into mortal sin, the grace of contrition would be given to him."