A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
est 8:1MORDECAI ADVANCED. (Est 8:1-6)
On that day did the king Ahasuerus give the house of Haman . . . unto Esther--His property was confiscated, and everything belonging to him, as some compensation for the peril to which she had been exposed.
Mordecai came before the king--that is, was introduced at court and appointed one of the seven counsellors. Esther displayed great prudence and address in acknowledging Mordecai's relation to her at the moment most fitted to be of eminent service to him.
est 8:2the king took off his ring, . . . and gave it unto Mordecai--By that act transferring to him all the power and authority which the ring symbolized, and promoting him to the high dignity which Haman had formerly filled.
Esther set Mordecai over the house of Haman--as her steward or factor, to manage that large and opulent estate which had been assigned to her.
est 8:3Esther spake yet again before the king, and fell down at his feet--The king was then not reclining at table, but sitting on a divan, most probably in the Persian attitude, leaning back against the cushions, and one foot under him.
besought him with tears to put away the mischief of Haman--that is, to repeal the sanguinary edict which, at the secret instigation of Haman, had been recently passed (Est 3:12).
est 8:4Then the king held out the golden sceptre toward Esther--in token that her request was accepted, and that she needed no longer to maintain the humble attitude of a suppliant.
est 8:5reverse the letters devised by Haman . . . to destroy the Jews--The whole conduct of Esther in this matter is characterized by great tact, and the variety of expressions by which she describes her willing submission to her royal husband, the address with which she rolls the whole infamy of the meditated massacre on Haman, and the argument she draws from the king's sanction being surreptitiously obtained, that the decree should be immediately reversed--all indicate the queen's wisdom and skill, and she succeeded in this point also.
est 8:8AHASUERUS GRANTS TO THE JEWS TO DEFEND THEMSELVES. (Est 8:7-14)
Write . . . in the king's name, and seal it with the king's ring--Hence it is evident that the royal ring had a seal in it, which, being affixed to any document, authenticated it with the stamp of royal authority.
which . . . may no man reverse--This is added as the reason why he could not comply with the queen's request for a direct reversal or recall of Haman's letters; namely, that the laws of the Medes and Persians, once passed, were irrevocable.
est 8:10sent . . . by posts . . . and riders on . . . camels, and young dromedaries--The business being very urgent, the swiftest kind of camel would be employed, and so the word in the original denotes the wind-camel. Young dromedaries also are used to carry expresses, being remarkable for the nimbleness and ease of their movements. Animals of this description could convey the new rescript of Ahasuerus over the length and breadth of the Persian empire in time to relieve the unhappy Jews from the ban under which they lay.
est 8:11the king granted the Jews . . . to stand for their life . . . to slay . . . all . . . that would assault them--The fixed and unalterable character claimed for Persian edicts often placed the king in a very awkward dilemma; for, however bitterly he might regret things done in a moment of haste and thoughtlessness, it was beyond even his power to prevent the consequences. This was the reason on account of which the king was laid under a necessity not to reverse, but to issue a contradictory edict; according to which it was enacted that if, pursuant to the first decree, the Jews were assaulted, they might, by virtue of the second, defend themselves and even slay their enemies. However strange and even ridiculous this mode of procedure may appear, it was the only one which, from the peculiarities of court etiquette in Persia, could be adopted. Instances occur in sacred (Dan 6:14), no less than profane, history. Many passages of the Bible attest the truth of this, particularly the well-known incident of Daniel's being cast into the den of lions, in conformity with the rash decree of Darius, though, as it afterwards appeared, contrary to the personal desire of that monarch. That the law of Persia has undergone no change in this respect, and the power of the monarch not less immutable, appear from many anecdotes related in the books of modern travellers through that country.
est 8:15MORDECAI'S HONORS, AND THE JEWS' JOY. (Est 8:15-17)
Mordecai went out . . . in royal apparel--He was invested with the khelaat of official honor. A dress of blue and white was held in great estimation among the Persians; so that Mordecai, whom the king delighted to honor, was in fact arrayed in the royal dress and insignia. The variety and the kind of insignia worn by a favorite at once makes known to the people the particular dignity to which he has been raised.