The meaning of each beatitude:
The word poor seems to represent an Aramaic 'ányâ (Hebrew 'anî), bent down, afflicted, miserable, poor; while meek is rather a synonym from the same root, 'ánwan (Hebrew 'ánaw), bending oneself down, humble, meek, gentle. Some scholars would attach to the former word also the sense of humility; others think of "beggars before God" humbly acknowledging their need of Divine help. But the opposition of "rich" (Luke 6:24) points especially to the common and obvious meaning, which, however, ought not to be confined to economical need and distress, but may comprehend the whole of the painful condition of the poor: their low estate, their social dependence, their defenceless exposure to injustice from the rich and the mighty. Besides the Lord's blessing, the promise of the heavenly kingdom is not bestowed on the actual external condition of such poverty. The blessed ones are the poor "in spirit", who by their free will are ready to bear for God's sake this painful and humble condition, even though at present they be actually rich and happy; while on the other hand, the really poor man may fall short of this poverty "in spirit."
Inasmuch as poverty is a state of humble subjection, the "poor in spirit", come near to the "meek", the subject of the second blessing. The anawim, they who humbly and meekly bend themselves down before God and man, shall "inherit the land" and possess their inheritance in peace. This is a phrase taken from Psalm 36:11, where it refers to the Promised Land of Israel, but here in the words of Christ, it is of course but a symbol of the Kingdom of Heaven, the spiritual realm of the Messiah. Not a few interpreters, however, understand "the earth". But they overlook the original meaning of Psalm 36:11, and unless, by a far-fetched expedient, they take the earth also to be a symbol of the Messianic kingdom, it will be hard to explain the possession of the earth in a satisfactory way.
The "mourning" in the Third Beatitude is in Luke (6:25) opposed to laughter and similar frivolous worldly joy. Motives of mourning are not to be drawn from the miseries of a life of poverty, abjection, and subjection, which are the very blessings of verse 3, but rather from those miseries from which the pious man is suffering in himself and in others, and most of all the tremendous might of evil throughout the world. To such mourners the Lord Jesus carries the comfort of the heavenly kingdom, "the consolation of Israel" (Luke 2:25) foretold by the prophets, and especially by the Book of Consolation of Isaias (11-16). Even the later Jews knew the Messiah by the name of Menahhem, Consoler. These three blessings, poverty, abjection, and subjection are a commendation of what nowadays are called the passive virtues: abstinence and endurance, and the Eighth Beatitude (verse 10) leads us back again to the teaching.
The others, however, demand a more active behaviour. First of all, "hunger and thirst" after justice: a strong and continuous desire of progress in religious and moral perfection, the reward of which will be the very fulfillment of the desire, the continuous growth in holiness.
From this interior desire a further step should be taken to acting to the works of "mercy", corporal and spiritual. Through these the merciful will obtain the Divine mercy of the Messianic kingdom, in this life and in the final judgment. The wonderful fertility of the Church in works and institutions of corporal and spiritual mercy of every kind shows the prophetical sense, not to say the creative power, of this simple word of the Divine Teacher.
According to biblical terminology, "cleanness of heart" (verse 8) cannot exclusively be found in interior chastity, nor even, as many scholars propose, in a general purity of conscience, as opposed to the Levitical, or legal, purity required by the Scribes and Pharisees. At least the proper place of such a blessing does not seem to be between mercy (verse 7) and peacemaking (verse 9), nor after the apparently more far-reaching virtue of hunger and thirst after justice. But frequently in the Old and New Testaments (Genesis 20:5; Job 33:3, Psalms 23:4 (24:4) and 72:1 (73:1); 1 Timothy 1:5; 2 Timothy 2:22) the "pure heart" is the simple and sincere good intention, the "single eye" of Matthew 6:22, and thus opposed to the unavowed by-ends of the Pharisees (Matthew 6:1-6, 16-18; 7:15; 23:5-7, 14) This "single eye" or "pure heart" is most of all required in the works of mercy (verse 7) and zeal (verse 9) in behalf of one's neighbor. And it stands to reason that the blessing, promised to this continuous looking for God's glory, should consist of the supernatural "seeing" of God Himself, the last aim and end of the heavenly kingdom in its completion.
The "peacemakers" (verse 9) are those who not only live in peace with others but moreover do their best to preserve peace and friendship among mankind and between God and man, and to restore it when it has been disturbed. It is on account of this godly work, "an imitating of God's love of man" as St. Gregory of Nyssa styles it, that they shall be called the sons of God, "children of your Father who is in heaven" (Matthew 5:45).
When after all this the pious disciples of Christ are repaid with ingratitude and even "persecution" (verse 10) it will be but a new blessing, "for theirs is the kingdom of heaven."
So, by an inclusion, not uncommon in biblical poetry, the last blessing goes back to the first and the second. The pious, whose sentiments and desires whose works and sufferings are held up before us, shall be blessed and happy by their share in the Messianic kingdom, here and hereafter. And viewed in the intermediate verses seem to express, in partial images of the one endless beatitude, the same possession of the Messianic salvation. The eight conditions required constitute the fundamental law of the kingdom, the very pith and marrow of Christian perfection. For its depth and breadth of thought, and its practical bearing on Christian life, the passage may be put on a level with the Decalogue in the Old, and the Lord's Prayer in the New Testament, and it surpassed both in its poetical beauty of structure.