Matthew 5:6

Blessed are they which do hunger and thirst after righteousness: for they shall be filled--"shall be saturated." "From this verse," says THOLUCK, "the reference to the Old Testament background ceases." Surprising! On the contrary, none of these beatitudes is more manifestly dug out of the rich mine of the Old Testament. Indeed, how could any one who found in the Old Testament "the poor in spirit," and "the mourners in Zion," doubt that he would also find those same characters also craving that righteousness which they feel and mourn their want of? But what is the precise meaning of "righteousness" here? Lutheran expositors, and some of our own, seem to have a hankering after that more restricted sense of the term in which it is used with reference to the sinner's justification before God. (See Jer 23:6; Isa 45:24; Rom 4:6; Co2 5:21). But, in so comprehensive a saying as this, it is clearly to be taken--as in Mat 5:10 also--in a much wider sense, as denoting that spiritual and entire conformity to the law of God, under the want of which the saints groan, and the possession of which constitutes the only true saintship. The Old Testament dwells much on this righteousness, as that which alone God regards with approbation (Psa 11:7; Psa 23:3; Psa 106:3; Pro 12:28; Pro 16:31; Isa 64:5, &c.).

— Jamieson-Fausset-Brown Commentary (public domain)