On that day…So begins the eleventh chapter of the Book of Prophet Isaiah. What follows is a description of what has been described as an ideal world, a world that we nostalgically identify with the state of the Garden of Eden prior to the fall. It is a description of a sinless world, a world in which creatures have knowledge of the Lord and have retained the original innocence of creation. It is a description of a world where creatures live in harmony and peace. However, inasmuch as the chapter describes the state of the created world prior to the fall, it is also a description of the world yet to be realized, a world to which we all look forward. It is a description of that world that will result when the peoples of the earth shall have sought out the Lord, when the nations of the world shall bow before the Lord their God. It is a description of an ideal world, yes, but it is a world that will be realized nonetheless. This is because  on that day, the Lord God shall appoint a special judge for the world. It will be the responsibility of this judge to shepherd the peoples of the world under their one Creator God. This judge will accomplish this because the Spirit of the Lord shall be upon him, and his mission will be the restoration of justice. 
When during these days of Advent the Church renews her ardent desire for the second coming of Christ, she is in effect looking ahead to the realization of the above described world. This is because Jesus Christ has been seen as the special judge who was to be appointed by God. While in his birth and resurrection he has certainly given new live to the world and set it on the path to full restoration, it is in the Second coming of Christ (understood as the deliverance of the created world from its present bondage to corruption [cf. Romans 8:21]) that will bring it to full cycle. This is why until it happens, we all await with longing for  that day of the Lord .