This is an exclamation that should be translated with whatever exclamation of emphasis you have in your language to make it sound natural. (See: [[rc://en/ta/man/translate/figs-exclamations]])
The abstract noun "faithfulness" can be translated with an adjective. Alternate translation: "because he remains faithful to his covenant forever" (See: [[rc://en/ta/man/translate/figs-abstractnouns]])