[ the Catechism of the Catholic Church ]

329 St. Augustine says: " 'Angel' is the name of their office, not of their nature. If you seek the name of their nature, it is 'spirit'; if you seek the name of their office, it is 'angel': from what they are, 'spirit', from what they do, 'angel'." [188]   With their whole beings the angels are servants and messengers of God. Because they "always behold the face of my Father, who is in heaven" they are the "mighty ones who do his word, harkening to the voice of his word." [189]

330 As purely spiritual creatures Angels have intelligence and will: they are personal and immortal creatures, surpassing in perfection all visible creatures, as the splendor of their glory bears witness. [190]

336 From it's beginning until death, human life is surrounded by their watchful care and intercession. [202]  "Beside each believer stands an angel as protector and shepherd leading him to life." [203]  Already here on earth the Christian life shares by faith in the blessed company of angels and men united in God.

[188] St. Augustine, En. in Ps. 103, 1, 15: PL 37, 1348.

[189] Mt 18:10; Ps 103:20.

[190] Cf. Pius XII Humani generis: DS 3891; Lk 20:36; Dan 10:9-12
[202] Cf. Mt 18:10; Lk 16:22; Ps 34:7; 91:10-13; Job 33:23-24; Zech 1:12; Tob 12:12.
[203] St. Basil, Adv. Eunomium III, 1: PG 29, 656B.

[ Servi Inutiles ]

Lk 17:10 " So you also, when you shall have done all these things that are commanded you, say: We are unprofitable servants; we have done that which we ought to do. "

[ "Unprofitable servants"... Because our service is of no profit to our master; and He justly claims it as our bounden duty. But though we are unprofitable to Him, our serving Him is not unprofitable to us; for He is pleased to give by His grace a value to our good works, which, in consequence of His promise, entitles them to an eternal reward. ]