By the end of The Children of Men by P.D. James, Theo Faron has changed significantly. He has long been emotionally detached from the people around him, a condition that stems back to his inability to cope with his father's death and the accidental death of his daughter, Natalie, whom Theo hit with his car. He has lived in near isolation for many years and does not want anyone to depend upon him for anything. He is not even all that interested in his profession as a history professor (although he is highly intelligent).
As the novel progresses, Theo is forced out of his comfort zone. He meets Julian and reluctantly becomes involved with the Five Fishes, the dissident group to which Julian belongs. The Five Fishes protest the tyrannical rule of Theo's cousin, Xan, the Warden of England, and the abuses the state has long since indulged in. At first, Theo wants nothing to do with this. He remains cynical about the group's idealism and rather arrogant toward them. Then, however, he personally witnesses a Quietus (the forced suicide of elderly people, including one woman whom he knows), and his views begin to change.
Theo still does not want to get involved and goes on a several month journey through Europe. When he returns, however, he discovers that Julian is pregnant. This does not seem like it should be such a big event, but there have been no children born in England since 1995 (the novel opens in 2021). Theo finds himself on the run with the Five Fishes, trying unsuccessfully to conceal Julian's pregnancy and stay one step ahead of the officials. Theo is quickly discovering what it means to put someone else's needs before his own. He is being pulled out of his selfish isolation. He even helps Julian as she gives birth to her child. Indeed, Theo is learning how to love. In a way, this is a spiritual change, for love always has a spiritual element to it.
However, at the end of the story, readers wonder about the depth of Theo's change. When Xan discovers Theo and Julian (who are the last members of the Five Fishes), he threatens and then tries to kill Theo. Theo shoots him instead. But then he does something else. He takes Xan's Coronation Ring, the symbol of absolute power in England, and he puts it on his own finger. He tells himself and Julian that he will rule only for a while until he can remedy the evils, but when Julian wonders why he put on the ring at all, he is irritated. This shows that Theo has been captured, at least a bit, by the lure of power that the ring symbolizes. His conversion to selfless love is not complete. It is still faulty and still vulnerable. Theo does make the sign of the cross on the baby's forehead, but he is still at risk of falling to temptation. If he has experienced a spiritual rebirth at all, it is limited and fragile.