Keep his covenant ... for a thousand generations

These two phrases share similar meanings and are used together for emphasis. Here "word" refers to the covenant. Alternate translation: "Keep his covenant in mind forever, the promise that he made for a thousand generations" (See: rc://en/ta/man/translate/figs-parallelism and rc://en/ta/man/translate/figs-metonymy)

Keep his covenant in mind

This means to remember and think about his covenant. Alternate translation: "Remember his covenant" (See: rc://en/ta/man/translate/figs-idiom)