Right throughout The Children of Men, Julian is shown as an admirable, heroic character. Passionately devoted to the cause of social justice, dedicated to bringing about the end of Xan Lyppiatt's despotic regime, Julian shows considerable courage in standing up for what's right.
In symbolic terms, Julian and the baby to which she gives birth towards the end of the book represent the chance of spiritual renewal in a society ravaged by evil. Now that Xan is no longer alive and the first baby for a quarter of a century has been born, England has a golden opportunity to move on from its sinful past and once more set foot on the path of righteousness.
Even so, the road ahead is by no means destined to be a smooth one. Theo's putting on of Xan's Coronation Ring is a potentially ominous sign that things may not change for the better, after all; that Theo may end up being every bit as much of a dictator as his cousin.
Julian spots the danger immediately, and once more displays her admirable and heroic nature by pointing out to Theo that the ring wasn't made for his finger. In any case, whatever her misgivings about Theo's actions, Julian remains steadfast in her commitment to the spiritual revival of England, as can be seen in her request that Theo christens her baby.