St. Thomas on Justification - Grace after a fall

In this series we have seen that St. Thomas consistently teaches us that a man can in no way merit the grace by which he is united to Christ. Well, what about the one who falls into mortal sin as a Christian? May he merit the grace of restoration by something that he might do? No.

It is written (Ezekiel 18:24): "If the just man turn himself away from his justice and do iniquity . . . all his justices which he hath done shall not be remembered." Therefore his previous merits will nowise help him to rise again. Hence no one can merit for himself restoration after a fall. [ST I-II, Q114, A7]

When we break fellowship with God, we break fellowship with God.

No one can merit for himself restoration after a future fall, either condignly or congruously. He cannot merit for himself condignly, since the reason of this merit depends on the motion of Divine grace, and this motion is interrupted by the subsequent sin; hence all benefits which he afterwards obtains from God, whereby he is restored, do not fall under merit--the motion of the preceding grace not extending to them. Again, congruous merit, whereby one merits the first grace for another, is prevented from having its effect on account of the impediment of sin in the one for whom it is merited. Much more, therefore, is the efficacy of such merit impeded by the obstacle which is in him who merits, and in him for whom it is merited; for both these are in the same person. And therefore a man can nowise merit for himself restoration after a fall.

We do not and cannot "deserve" to be reconciled to God.