Objection 1. It would seem that poverty of spirit is not the beatitude corresponding to the gift of fear. For fear is the beginning of the spiritual life, as explained above (Article 7): whereas poverty belongs to the perfection of the spiritual life, according to Matthew 19:21, "If thou wilt be perfect, go sell what thou hast, and give to the poor." Therefore poverty of spirit does not correspond to the gift of fear.
Objection 2. Further, it is written (Psalm 118:120): "Pierce Thou my flesh with Thy fear," whence it seems to follow that it belongs to fear to restrain the flesh. But the curbing of the flesh seems to belong rather to the beatitude of mourning. Therefore the beatitude of mourning corresponds to the gift of fear, rather than the beatitude of poverty.
Objection 3. Further, the gift of fear corresponds to the virtue of hope, as stated above (9, ad 1). Now the last beatitude which is, "Blessed are the peacemakers, for they shall be called the children of God," seems above all to correspond to hope, because according to Romans 5:2, "we... glory in the hope of the glory of the sons of God." Therefore that beatitude corresponds to the gift of fear, rather than poverty of spirit.
Objection 4. Further, it was stated above (I-II, 70, 2) that the fruits correspond to the beatitudes. Now none of the fruits correspond to the gift of fear. Neither, therefore, does any of the beatitudes.
On the contrary, Augustine says (De Serm. Dom. in Monte i, 4): "The fear of the Lord is befitting the humble of whom it is said: Blessed are the poor in spirit."
I answer that, Poverty of spirit properly corresponds to fear. Because, since it belongs to filial fear to show reverence and submission to God, whatever results from this submission belongs to the gift of fear. Now from the very fact that a man submits to God, it follows that he ceases to seek greatness either in himself or in another but seeks it only in God. For that would be inconsistent with perfect subjection to God, wherefore it is written (Psalm 19:8): "Some trust in chariots and some in horses; but we will call upon the name of... our God." It follows that if a man fear God perfectly, he does not, by pride, seek greatness either in himself or in external goods, viz. honors and riches. On either case, this proceeds from poverty of spirit, in so far as the latter denotes either the voiding of a puffed up and proud spirit, according to Augustine's interpretation (De Serm. Dom. in Monte i, 4), or the renunciation of worldly goods which is done in spirit, i.e. by one's own will, through the instigation of the Holy Spirit, according to the expounding of Ambrose on Luke 6:20 and Jerome on Matthew 5:3.
Reply to Objection 1. Since a beatitude is an act of perfect virtue, all the beatitudes belong to the perfection of spiritual life. And this perfection seems to require that whoever would strive to obtain a perfect share of spiritual goods, needs to begin by despising earthly goods, wherefore fear holds the first place among the gifts. Perfection, however, does not consist in the renunciation itself of temporal goods; since this is the way to perfection: whereas filial fear, to which the beatitude of poverty corresponds, is consistent with the perfection of wisdom, as stated above (A7,10).
Reply to Objection 2. The undue exaltation of man either in himself or in another is more directly opposed to that submission to God which is the result of filial fear, than is external pleasure. Yet this is, in consequence, opposed to fear, since whoever fears God and is subject to Him, takes no delight in things other than God. Nevertheless, pleasure is not concerned, as exaltation is, with the arduous character of a thing which fear regards: and so the beatitude of poverty corresponds to fear directly, and the beatitude of mourning, consequently.
Reply to Objection 3. Hope denotes a movement by way of a relation of tendency to a term, whereas fear implies movement by way of a relation of withdrawal from a term: wherefore the last beatitude which is the term of spiritual perfection, fittingly corresponds to hope, by way of ultimate object; while the first beatitude, which implies withdrawal from external things which hinder submission to God, fittingly corresponds to fear.
Reply to Objection 4. As regards the fruits, it seems that those things correspond to the gift of fear, which pertain to the moderate use of temporal things or to abstinence therefrom; such are modesty, continency and chastity.
Source: Summa Theologica (New Advent)