6 “Blessed are they which do hunger and thirst after righteousness.”
What sort of righteousness? He means either the whole of virtue, or that particular virtue which is opposed to covetousness. For since He is about to give commandment concerning mercy, to show how we must show mercy, as, for instance, not of rapine or covetousness, He blesses them that lay hold of righteousness.
And see with what exceeding force He puts it. For He said not, “Blessed are they which keep fast by righteousness,” but, “Blessed are they which do hunger and thirst after righteousness:” that not merely anyhow, but with all desire we may pursue it. For since this is the most peculiar property of covetousness, and we are not so enamored of meat and drink, as of gaining, and compassing ourselves with more and more, He bade us to transfer this desire to a new object, freedom from covetousness.
Then He appoints the prize, again from things sensible; saying, “for they shall be filled.” Thus, because it is thought that the rich are commonly made such by covetousness, “Nay,” says He, “it is just contrary: for it is righteousness that does this. Wherefore, so long as you do righteously, fear not poverty, nor tremble at hunger. For the extortioners, they are the very persons who lose all, even as he certainly who is in love with righteousness, possesses himself the goods of all men in safety.”
But if they who covet not other men's goods enjoy so great abundance, much more they who give up their own.
“Blessed are the merciful.”
Here He seems to me to speak not of those only who show mercy in giving of money, but those likewise who are merciful in their actions. For the way of showing mercy is manifold, and this commandment is broad. What then is the reward thereof? “For they shall obtain mercy.”
And it seems indeed to be a sort of equal recompence, but it is a far greater thing than the act of goodness. For whereas they themselves show mercy as men, they obtain mercy from the God of all; and it is not the same thing, man's mercy, and God's; but as wide as is the interval between wickedness and goodness, so far is the one of these removed from the other.
“Blessed are the pure in heart, for they shall see God.”
Behold again the reward is spiritual. Now He here calls “pure,” either those who have attained unto all virtue, and are not conscious to themselves of any evil; or those who live in temperance. For there is nothing which we need so much in order to see God, as this last virtue. Wherefore Paul also said, “Follow peace with all men, and holiness, without which no man shall see the Lord.” He is here speaking of such sight as it is possible for man to have.
For because there are many who show mercy, and who commit no rapine, nor are covetous, who yet are guilty of fornication and uncleanness; to signify that the former alone suffices not, He has added this, much in the same sense as Paul, writing to the Corinthians, bore witness of the Macedonians, that they were rich not only in almsgiving, but also in all other virtue. For having spoken of the noble spirit they had shown in regard of their goods, he says, “They gave also their own selves to the Lord, and to us.”
Source: Homilies on the Gospel of St. Matthew (New Advent)