“he will fill.” The Hebrew uses the prophetic perfect idiom, and reads, “he has filled.” The prophetic perfect was a common way that a future event that was sure to come to pass was expressed in the Hebrew language—by saying it had already happened. [For more on the prophetic perfect idiom, see commentary on Ephesians 2:6].
“righteousness.” In this context, “righteousness” is doing what is right toward God and people, and in effect is “justice.” In Isaiah 33:5, “justice” means more like “judgment,” that is fair judgment, thus justice. The emphasis is the effect: justice. In contrast, “righteousness” has more emphasis on the action; doing what is right to God and to fellow humans. There is no justice on earth now, but there will be in Christ’s Millennial Kingdom on earth. Christ will reign in righteousness, doing the right and just thing, and the effect of that will be peace, quietness, and confidence. [For more on “righteousness” having the meaning of doing what is right or just (“justice”), see commentary on Matt. 5:6. For more on Christ’s future Millennial Kingdom on earth, see Appendix 3, “Christ’s Future Kingdom on Earth”].