Objection 1. It would seem that the rewards assigned to the beatitudes do not refer to this life. Because some are said to be happy because they hope for a reward, as stated above (Article 1). Now the object of hope is future happiness. Therefore these rewards refer to the life to come.
Objection 2. Further, certain punishments are set down in opposition to the beatitudes, Luke 6:25, where we read: "Woe to you that are filled; for you shall hunger. Woe to you that now laugh, for you shall mourn and weep." Now these punishments do not refer to this life, because frequently men are not punished in this life, according to Job 21:13: "They spend their days in wealth." Therefore neither do the rewards of the beatitudes refer to this life.
Objection 3. Further, the kingdom of heaven which is set down as the reward of poverty is the happiness of heaven, as Augustine says (De Civ. Dei xix) [Cf. De Serm. Dom. in Monte i, 1. Again, abundant fullness is not to be had save in the life to come, according to Psalm 16:15: "I shall be filled [Douay: 'satisfied'] when Thy glory shall appear." Again, it is only in the future life that we shall see God, and that our Divine sonship will be made manifest, according to 1 John 3:2: "We are now the sons of God; and it hath not yet appeared what we shall be. We know that, when He shall appear, we shall be like to Him, because we shall see Him as He is." Therefore these rewards refer to the future life.
On the contrary, Augustine says (De Serm. Dom. in Monte i, 4): "These promises can be fulfilled in this life, as we believe them to have been fulfilled in the apostles. For no words can express that complete change into the likeness even of an angel, which is promised to us after this life."
I answer that, Expounders of Holy Writ are not agreed in speaking of these rewards. For some, with Ambrose (Super Luc. v), hold that all these rewards refer to the life to come; while Augustine (De Serm. Dom. in Monte i, 4) holds them to refer to the present life; and Chrysostom in his homilies (In Matth. xv) says that some refer to the future, and some to the present life.
In order to make the matter clear we must take note that hope of future happiness may be in us for two reasons. First, by reason of our having a preparation for, or a disposition to future happiness; and this is by way of merit; secondly, by a kind of imperfect inchoation of future happiness in holy men, even in this life. For it is one thing to hope that the tree will bear fruit, when the leaves begin to appear, and another, when we see the first signs of the fruit.
Accordingly, those things which are set down as merits in the beatitudes, are a kind of preparation for, or disposition to happiness, either perfect or inchoate: while those that are assigned as rewards, may be either perfect happiness, so as to refer to the future life, or some beginning of happiness, such as is found in those who have attained perfection, in which case they refer to the present life. Because when a man begins to make progress in the acts of the virtues and gifts, it is to be hoped that he will arrive at perfection, both as a wayfarer, and as a citizen of the heavenly kingdom.
Reply to Objection 1. Hope regards future happiness as the last end: yet it may also regard the assistance of grace as that which leads to that end, according to Psalm 27:7: "In Him hath my heart hoped, and I have been helped."
Reply to Objection 2. Although sometimes the wicked do not undergo temporal punishment in this life, yet they suffer spiritual punishment. Hence Augustine says (Confess. i): "Thou hast decreed, and it is so, Lord--that the disordered mind should be its own punishment." The Philosopher, too, says of the wicked (Ethic. ix, 4) that "their soul is divided against itself... one part pulls this way, another that"; and afterwards he concludes, saying: "If wickedness makes a man so miserable, he should strain every nerve to avoid vice." In like manner, although, on the other hand, the good sometimes do not receive material rewards in this life, yet they never lack spiritual rewards, even in this life, according to Matthew 19:29, and Mark 10:30: "Ye shall receive a hundred times as much" even "in this time."
Reply to Objection 3. All these rewards will be fully consummated in the life to come: but meanwhile they are, in a manner, begun, even in this life. Because the "kingdom of heaven," as Augustine says (De Civ. Dei xiv; Cf. De Serm. Dom. in Monte, i, 1), can denote the beginning of perfect wisdom, in so far as "the spirit" begins to reign in men. The "possession" of the land denotes the well-ordered affections of the soul that rests, by its desire, on the solid foundation of the eternal inheritance, signified by "the land." They are "comforted" in this life, by receiving the Holy Ghost, Who is called the "Paraclete," i.e. the Comforter. They "have their fill," even in this life, of that food of which Our Lord said (John 4:34): "My meat is to do the will of Him that sent Me." Again, in this life, men "obtain" God's "Mercy." Again, the eye being cleansed by the gift of understanding, we can, so to speak, "see God." Likewise, in this life, those who are the "peacemakers" of their own movements, approach to likeness to God, and are called "the children of God." Nevertheless these things will be more perfectly fulfilled in heaven.
Source: Summa Theologica (New Advent)