Question Four of Chapter Four of the Second Decade
On the beginning and end of the guardianship of angels
It is asked: in what state does the guardianship of angels begin, and at what time is it ended?
To this it is answered as follows. The guardianship of angels begins immediately when the creature is born by the first birth, namely outside the womb.
The reason is that guardianship ought to be applied when danger to the salvation of the soul is feared.
But after the creature is born, danger to the salvation of the soul is feared, because, as the Psalm says, “In the way in which I walked, they hid a snare for me”; and then the world, the flesh, and the demons begin to stir up new battles.
Before the creature leaves the womb, however, guardianship is not given, because then, since such children are still something of the mother, they are guarded by the mother’s angel, as has been said.
This guardianship endures inclusively until death, because after death they do not need guardianship.
For if they are in the fatherland, they no longer fear being endangered. Isaiah, chapter 60, says: “Your sun shall no more set, and your moon shall not decrease, because the Lord will be for you an everlasting light, and the days of your mourning shall be completed.”
If they are in hell, they do not fear being endangered, because the fear which they feared has come upon them.
Nor [do they need guardianship] in purgatory, since they are outside the limit of meriting and demeriting and cannot recoil from grace itself.
Thus guardianship is given on the way and not after the course is completed.
See Thomas, First Part, question 113, and the Master of the Sentences, distinction 11.