Objection 1. It would seem that fear is unfittingly divided into filial, initial, servile and worldly fear. For Damascene says (De Fide Orth. ii, 15) that there are six kinds of fear, viz. "laziness, shamefacedness," etc. of which we have treated above (I-II, 41, 4), and which are not mentioned in the division in question. Therefore this division of fear seems unfitting.
Objection 2. Further, each of these fears is either good or evil. But there is a fear, viz. natural fear, which is neither morally good, since it is in the demons, according to James 2:19, "The devils... believe and tremble," nor evil, since it is in Christ, according to Mark 14:33, Jesus "began to fear and be heavy." Therefore the aforesaid division of fear is insufficient.
Objection 3. Further, the relation of son to father differs from that of wife to husband, and this again from that of servant to master. Now filial fear, which is that of the son in comparison with his father, is distinct from servile fear, which is that of the servant in comparison with his master. Therefore chaste fear, which seems to be that of the wife in comparison with her husband, ought to be distinguished from all these other fears.
Objection 4. Further, even as servile fear fears punishment, so do initial and worldly fear. Therefore no distinction should be made between them.
Objection 5. Further, even as concupiscence is about some good, so is fear about some evil. Now "concupiscence of the eyes," which is the desire for things of this world, is distinct from "concupiscence of the flesh," which is the desire for one's own pleasure. Therefore "worldly fear," whereby one fears to lose external goods, is distinct from "human fear," whereby one fears harm to one's own person.
On the contrary stands the authority of the Master (Sent. iii, D, 34).
I answer that, We are speaking of fear now, in so far as it makes us turn, so to speak, to God or away from Him. For, since the object of fear is an evil, sometimes, on account of the evils he fears, man withdraws from God, and this is called human fear; while sometimes, on account of the evils he fears, he turns to God and adheres to Him. This latter evil is twofold, viz. evil of punishment, and evil of fault.
Accordingly if a man turn to God and adhere to Him, through fear of punishment, it will be servile fear; but if it be on account of fear of committing a fault, it will be filial fear, for it becomes a child to fear offending its father. If, however, it be on account of both, it will be initial fear, which is between both these fears. As to whether it is possible to fear the evil of fault, the question has been treated above (I-II, 42, 3) when we were considering the passion of fear.
Reply to Objection 1. Damascene divides fear as a passion of the soul: whereas this division of fear is taken from its relation to God, as explained above.
Reply to Objection 2. Moral good consists chiefly in turning to God, while moral evil consists chiefly in turning away from Him: wherefore all the fears mentioned above imply either moral evil or moral good. Now natural fear is presupposed to moral good and evil, and so it is not numbered among these kinds of fear.
Reply to Objection 3. The relation of servant to master is based on the power which the master exercises over the servant; whereas, on the contrary, the relation of a son to his father or of a wife to her husband is based on the son's affection towards his father to whom he submits himself, or on the wife's affection towards her husband to whom she binds herself in the union of love. Hence filial and chaste fear amount to the same, because by the love of charity God becomes our Father, according to Romans 8:15, "You have received the spirit of adoption of sons, whereby we cry: Abba [Father]"; and by this same charity He is called our spouse, according to 2 Corinthians 11:2, "I have espoused you to one husband, that I may present you as a chaste virgin to Christ": whereas servile fear has no connection with these, since it does not include charity in its definition.
Reply to Objection 4. These three fears regard punishment but in different ways. For worldly or human fear regards a punishment which turns man away from God, and which God's enemies sometimes inflict or threaten: whereas servile and initial fear regard a punishment whereby men are drawn to God, and which is inflicted or threatened by God. Servile fear regards this punishment chiefly, while initial fear regards it secondarily.
Reply to Objection 5. It amounts to the same whether man turns away from God through fear of losing his worldly goods, or through fear of forfeiting the well-being of his body, since external goods belong to the body. Hence both these fears are reckoned as one here, although they fear different evils, even as they correspond to the desire of different goods. This diversity causes a specific diversity of sins, all of which alike however lead man away from God.
Source: Summa Theologica (New Advent)