"Righteousness" has an internal meaning that is very similar to that of "meek"; it has to do with the love of doing good things for other people. In the prior verse, then, the Lord addressed those who were already in that state; here He addresses those who "hunger and thirst" for that state.

Hunger represents the desire to want what's good, despite the craving for what is evil (sort of, "I'd like to be craving celery right now, despite the fact that I'm actually craving chocolate ice cream"). Thirst represents a lack of knowledge about what is good, and a desire to learn.

This verse, then, says that those who want to resist evil and delight in being good instead, and who want to learn what they need to know to make that change, will get what they're seeking.

4048. There was a certain spirit close to my head who spoke to me. From the sound I perceived that his state was a state of tranquillity, like that of a peaceful sleep. He asked about this and that, but so cautiously that someone wide awake could not have displayed greater caution. I perceived that interior angels spoke through him, and that his state was one in which he perceived and reproduced what they said. I made some inquiries about that state and then I told him that the nature of it was as I had perceived it. He replied that he did not speak anything other than what was good and true, and that he detected whether anything else was present; and if anything other came along he did not entertain it or utter it. In reference to his state he said that it was peaceful, as I was also allowed to perceive through the communication of it to me. I was told that of such a nature were the spirits who correlate with the sinuses or major blood vessels in the brain, and that those who were like that particular spirit correlate with the longitudinal sinus which lies between the two hemispheres of the brain, and in a quiet state there even though the brain on either side of it may be in utter turmoil.