Haydock links the meekness Beatitude to Jesus’ fulfilment of the law described by David in beautiful Psalm 36 “But the meek shall inherit the land, and shall delight in abundance of peace.” Jesus announces his completion of those promises in the higher land – the kingdom of heaven for those of humble heart and selfless love – the meek. Although not addressed directly in this passage, the meek are not the weak. The meek heart often is the final stage of great strength and courage through trials – ie Moses.
Here is Haydock:
“'Ver. 4. The land of the living, or the kingdom of heaven. The evangelist prefers calling it the land of the living in this place, to shew that the meek, the humble, and the oppressed, who are spoiled of the possession of this earth by the powerful and the proud, shall obtain the inheritance of a better land. (Menochius) “They shall possess the land,” is the reward annexed by our Saviour to meekness, that he might not differ in any point from the old law, so well known to the persons he was addressing. David, in psalm xxxvi, had made the same promise to the meek. If temporal blessings are promised to some of the virtues in the beatitudes, it is that temporal blessings might always accompany the more solid rewards of grace. But spiritual rewards are always the principal, always ranked in the first place, all who practice these virtues are pronounced blessed. (Hom. xv)”