In the Sermon on the Mount the benediction is pronounced upon the "poor in spirit" and those who "hunger and thirst after righteousness" (Mt 5:3, 6). Here it is simply on the "poor" and the "hungry now." In this form of the discourse, then, our Lord seems to have had in view "the poor of this world, rich in faith, and heirs of the kingdom which God hath promised to them that love Him," as these very beatitudes are paraphrased by James (Jas 2:5).
It is true, neither riches nor poverty bless or curse any man, and none that are poor are blessed if they be proud and high minded, nor any rich man cursed but he that places his portion or consolation in riches; yet Christ here, by the antithesis, seems more particularly to direct his discourse to relieve his disciples discouraged by their poor and low estate in the world, by telling them that, whatever the world thought, they, being his disciples, believing in him, and following him, were in a better condition than those that were rich, and had their consolation in this life.
The foundation characteristic is poverty of spirit, the consciousness of one’s own weakness, the opposite of the delusion that we are ‘rich and increased with goods.’ All true subjection to the kingdom begins with that accurate, because lowly, estimate of ourselves. Humility is life, lofty mindedness is death. The heights are barren, rivers and fertility are down in the valleys.
[Excerpt from Jamieson-Fausset-Brown Bible Commentary, Matthew Poole's Commentary, & MacLaren's Expositions