So speak and act

"So you must speak and obey." James commanded the people to do this.

who will be judged by means of the law of freedom

This can be stated in active form. AT: "who know that God will judge them by means of the law of freedom" (See: rc://en/ta/man/translate/figs-activepassive)

This passage implies that it is God who will judge according to his law.

"the law that gives true freedom"

"Mercy is better than" or "Mercy defeats." Here mercy and justice are spoken of as if they were persons. (See: rc://en/ta/man/translate/figs-personification)