# did not appreciate your marvelous deeds

"were not grateful for the marvelous deed you did"

# they ignored your many acts of covenant faithfulness

The abstract noun "faithfulness" can be translated with an adjective. Alternate translation: "they ignored the many things that you did because you are faithful to your covenant" (See: [[rc://en/ta/man/translate/figs-abstractnouns]])

# at the sea ... the Sea of Reeds

These two phrases refer to the same sea. The second is the name of the sea.