The fear of the LORD is clean, enduring for ever: the judgments of the LORD are true and righteous altogether. (KJV)
The law and the word of the LORD is what brings about the fear of the LORD. This fear is clean or "pure" and it never ends. The judgments(ordinances or decisions) never contradict themselves. Every law is always 100% true and 100% righteous. They have no flaws. David wrote "altogether" so no one could exclude one of the laws. In the last day, GOD will judge every man, and we should be very fearful of HIM because of the purity of HIS judgments. GOD is the ultimate judge, HE has never falsely accused someone or wrongly judged them. That's why its so important to get the point across of how holy, pure and perfect GOD is. Not GOD alone, but everything HE says and does.