This section of the poem foretells Satan’s restriction to the spirit world of hell during the millennial years of peace on earth and describes the reaction of hell’s inhabitants when it is announced that he is assigned there. The bolded retention (v. 11, not in the KJV) clarifies the text.
That Satan will have influence in the spirit world is shown by the Prophet Joseph Smith’s statement that “when we have power to put all enemies under our feet in this world, and a knowledge to triumph over evil spirits in the world to come, then we are saved” (TPJS, 297). Amulek also warned of the devils power there:
34 Ye cannot say, when ye are brought to that awful crisis, that I will repent, that I will return to my God. Nay, ye cannot say this; for that same spirit which doth possess your bodies at the time that ye go out of this life, that same spirit will have power to possess your body in that eternal world.
35 For behold, if ye have procrastinated the day of your repentance even until death, behold, ye have become subjected to the spirit of the devil, and he doth seal you his; therefore, the Spirit of the Lord hath withdrawn from you, and hath no place in you, and the devil hath all power over you; and this is the final state of the wicked. (Alma 34:34–35)
When Satan is bound in the spirit world, “the chief ones of the earth”—those leaders who were influential in the devil’s kingdom while they lived upon the earth—will assemble to greet him. When they see him, they will be amazed at his having lost his power (v. 10).