The abstract noun "faithfulness" can be translated with an adjective. AT: "Because you are good and are faithful to your covenant" (See: [[rc://en/ta/man/translate/figs-abstractnouns]])
These two words have similar meanings and emphasize that he is unable to help himself. (See: [[rc://en/ta/man/translate/figs-doublet]])
# my heart is wounded within me
Here David speaks of being in great despair as his heart being wounded. AT: "I am full of grief and despair" (See: [[rc://en/ta/man/translate/figs-metaphor]])
# I am fading away like the shadow ... like a locust
David feels like he is going to die soon and describes this feeling by comparing himself to a fading shadow and to how the wind blows away locust. AT: "I feel like I am about to die, like an evening shadow that will soon disappear, like a locust is easily blown away by the wind" (See: [[rc://en/ta/man/translate/figs-metaphor]])