Here David compares how Yahweh cares for his people to how a shepherd cares for his sheep. Possible meanings are 1) "makes the number of people in their families increase like flocks" or 2) "takes care of them like a shepherd cares for his sheep" (See: [[rc://en/ta/man/translate/figs-simile]])
This refers to people who live in an upright way. AT: "Upright people" or "People who do what is right" (See: [[rc://en/ta/man/translate/figs-nominaladj]])
The abstract noun "faithfulness" can be translated with an adjective. AT: "meditate on the things that Yahweh has done that show that he is faithful to his covenant" (See: [[rc://en/ta/man/translate/figs-abstractnouns]])