Objection 1. It would seem that the fifth beatitude, which is that of mercy, does not correspond to the gift of counsel. For all the beatitudes are acts of virtue, as stated above (I-II, 69, 1). Now we are directed by counsel in all acts of virtue. Therefore the fifth beatitude does not correspond more than any other to counsel.
Objection 2. Further, precepts are given about matters necessary for salvation, while counsel is given about matters which are not necessary for salvation. Now mercy is necessary for salvation, according to James 2:13, "Judgment without mercy to him that hath not done mercy." On the other hand poverty is not necessary for salvation, but belongs to the life of perfection, according to Matthew 19:21. Therefore the beatitude of poverty corresponds to the gift of counsel, rather than to the beatitude of mercy.
Objection 3. Further, the fruits result from the beatitudes, for they denote a certain spiritual delight resulting from perfect acts of virtue. Now none of the fruits correspond to the gift of counsel, as appears from Galatians 5:22-23. Therefore neither does the beatitude of mercy correspond to the gift of counsel.
On the contrary, Augustine says (De Serm. Dom. iv): "Counsel is befitting the merciful, because the one remedy is to be delivered from evils so great, to pardon, and to give."
I answer that, Counsel is properly about things useful for an end. Hence such things as are of most use for an end, should above all correspond to the gift of counsel. Now such is mercy, according to 1 Timothy 4:8, "Godliness ['Pietas,' which our English word 'pity,' which is the same as mercy; see note on II-II, 30, 1 is profitable to all things." Therefore the beatitude of mercy specially corresponds to the gift of counsel, not as eliciting but as directing mercy.
Reply to Objection 1. Although counsel directs in all the acts of virtue, it does so in a special way in works of mercy, for the reason given above.
Reply to Objection 2. Counsel considered as a gift of the Holy Ghost guides us in all matters that are directed to the end of eternal life whether they be necessary for salvation or not, and yet not every work of mercy is necessary for salvation.
Reply to Objection 3. Fruit denotes something ultimate. Now the ultimate in practical matters consists not in knowledge but in an action which is the end. Hence nothing pertaining to practical knowledge is numbered among the fruits, but only such things as pertain to action, in which practical knowledge is the guide. Among these we find "goodness" and "benignity" which correspond to mercy.
Source: Summa Theologica (New Advent)