The word "throne" is a metonym for the deeds and words of the one who sits on it. The psalmist speaks as if righteousness and justice were physical objects that made the throne secure. Alternate translation: "He is righteous and just in everything he does" or "He is able to rule because he rules righteously and justly" (See: [[rc://en/ta/man/translate/figs-metonymy]] and [[rc://en/ta/man/translate/figs-metaphor]])