Luke 6:20

Blessed are ye poor... in spirit (See S. Mat 5:3), for poorness of spirit is a rich and precious virtue. Therefore S. Ambrose rightly concludes that poverty, privations, and sorrow, which the world counts evil, not only are no hindrances, but on the contrary have been declared by Him who could neither deceive nor be deceived, to be of great assistance towards the attainment of a holy and a happy life.

The same writer goes on to give the reason why S. Luke has reduced the number of the beatitudes to four. He was content that they should include the four cardinal virtues. Justice, which, coveting not the possessions of others, rejoices in holy poverty; temperance, which had rather suffer want than be full; prudence, which chooses to sorrow here, in hope of the joy which shall be revealed; and Fortitude, which for sake of Christ and His Gospel, endures persecution and so triumphs over every enemy. Hence we read that the poor, the temperate, those who hunger and thirst after righteousness (S. Matthew), the just, those who weep, the prudent who despise earthly things and seek heavenly, those hated of their fellowmen, not because of any misdeeds but for the Gospel's sake, who, steadfast in the faith, seek for future happiness by pleasing God rather than men that these are indeed blessed.