Objection 1. It would seem that angels grieve for the ills of those whom they guard. For it is written (Isaiah 33:7): "The angels of peace shall weep bitterly." But weeping is a sign of grief and sorrow. Therefore angels grieve for the ills of those whom they guard.
Objection 2. Further, according to Augustine (De Civ. Dei xiv, 15), "sorrow is for those things that happen against our will." But the loss of the man whom he has guarded is against the guardian angel's will. Therefore angels grieve for the loss of men.
Objection 3. Further, as sorrow is contrary to joy, so penance is contrary to sin. But angels rejoice about one sinner doing penance, as we are told, Luke 15:7. Therefore they grieve for the just man who falls into sin.
Objection 4. Further, on Numbers 18:12: "Whatsoever first-fruits they offer," etc. the gloss of Origen says: "The angels are brought to judgment as to whether men have fallen through their negligence or through their own fault." But it is reasonable for anyone to grieve for the ills which have brought him to judgment. Therefore angels grieve for men's sins.
On the contrary, Where there is grief and sorrow, there is not perfect happiness: wherefore it is written (Apocalypse 21:4): "Death shall be no more, nor mourning, nor crying, nor sorrow." But the angels are perfectly happy. Therefore they have no cause for grief.
I answer that, Angels do not grieve, either for sins or for the pains inflicted on men. For grief and sorrow, according to Augustine (De Civ. Dei xiv, 15) are for those things which occur against our will. But nothing happens in the world contrary to the will of the angels and the other blessed, because they will cleaves entirely to the ordering of Divine justice; while nothing happens in the world save what is effected or permitted by Divine justice. Therefore simply speaking, nothing occurs in the world against the will of the blessed. For as the Philosopher says (Ethic. iii, 1) that is called simply voluntary, which a man wills in a particular case, and at a particular time, having considered all the circumstances; although universally speaking, such a thing would not be voluntary: thus the sailor does not will the casting of his cargo into the sea, considered universally and absolutely, but on account of the threatened danger of his life, he wills it. Wherefore this is voluntary rather than involuntary, as stated in the same passage. Therefore universally and absolutely speaking the angels do not will sin and the pains inflicted on its account: but they do will the fulfilment of the ordering of Divine justice in this matter, in respect of which some are subjected to pains and are allowed to fall into sin.
Reply to Objection 1. These words of Isaias may be understood of the angels, i.e. the messengers, of Ezechias, who wept on account of the words of Rabsaces, as related Isaiah 37:2 seqq.: this would be the literal sense. According to the allegorical sense the "angels of peace" are the apostles and preachers who weep for men's sins. If according to the anagogical sense this passage be expounded of the blessed angels, then the expression is metaphorical, and signifies that universally speaking the angels will the salvation of mankind: for in this sense we attribute passions to God and the angels.
The reply to the second objection appears from what has been said.
Reply to Objection 3. Both in man's repentance and in man's sin there is one reason for the angel's joy, namely the fulfilment of the ordering of the Divine Providence.
Reply to Objection 4. The angels are brought into judgment for the sins of men, not as guilty, but as witnesses to convict man of weakness.
Source: Summa Theologica (New Advent)