"Lord, you are my God; I will exalt you and praise your name, for in perfect faithfulness you have done wonderful things, things planned long ago." NIV translation
This song begins with the acknowledgement that there really only is one God and He is in control. In Hebrew, the "wonderful things" is "pele" which actually speaks of a miracle. In this case, it is talking about the miracle of Jesus Christ stepping in and defeating the armies of the earth that were led by Satan. We also see that this victory was a part of God's plan from the beginning of time and that He kept His promise to deliver His people. When delivered from a situation such as the approach of this tremendous army led by Satan, the normal reaction is to celebrate the victory and sing about it. It was indeed a miracle as there was a huge army attacking Jerusalem and, with a word from His mouth, the army was slain. (see Revelation 19)
Isaiah 25:2 & 3
"You have made the city a heap of rubble, the fortified town a ruin, the foreigners stronghold a city no more; it will never be rebuilt. Therefore strong peoples will honor you; cities of ruthless nations will revere you." NIV translation
We do not exactly know what specific cities are being talked about here but we can make some educated guesses. They are probably the capitol cities of the nations as well as a chief city that was the headquarters of the world government that was set up and ran by the beast. We do not know the name of this chief city but it will be a city that is completely destroyed by the hand of God. The people from these nations will now be forced to acknowledge the hand of God and the fact that Jerusalem is His chief city.
Isaiah 25:4 & 5
"You have been a refuge for the poor, a refuge for the needy in distress, a shelter from the storm and a shade from the heat. For the breath of the ruthless is like a storm driving against a wall and like the heat of the desert. You silence the uproar of foreigners; as heat is reduced by the shadow of a cloud, so the song of the ruthless is stilled." NIV translation
The song continues with rejoicing over the fact that man's schemes have failed and Jerusalem is now a haven for God's children. The word that is translated here as "have been" is "hayah" and it actually means more like "have become".
This speaks to the fact that the remnant of God's people suffered tremendous persecution under the world system but, now, they are taken care of by Jesus Christ who reigns from Jerusalem. The "song of the ruthless" speaks of the lie that man could band together to overcome the will of God for His city and people.
"On this mountain the Lord Almighty will prepare a feast of rich food for all peoples, a banquet of aged wine - the best of meats and the finest of wines." NIV translation
This period will be a time when the nations bring their best to Jerusalem in honor of the Lord. This feast is a stark contrast to the time of suffering and shortage that the world has just been through. The bringing of their best into Jerusalem is a sign of acknowledgement that Jesus is, in fact, the King of Kings.
Isaiah 25:7 & 8
"On this mountain he will destroy the shroud that enfolds all peoples, the sheet that covers all nations; he will swallow up death forever. The Sovereign Lord will wipe away the tears from all faces; he will remove his people's disgrace from all the earth. The Lord has spoken." NIV translation
The final part of this song begins with praise for the fact that the shame and mourning of God's people has been removed and there is great joy. There will be no more death for His people and no more sorrow as they are a bright and shining example for the rest of the world.
"In that day they will say, 'Surely this is our God; we trusted in him, and he saved us. This is the Lord, we trusted in him; let us rejoice and be glad in his salvation.'" NIV translation
The people of God will sing and dance for joy as they celebrate the day that they had waited on for many years. They will rejoice in the fact that God has removed the shame from His people.
"The hand of the Lord will rest on this mountain; but Moab will be trampled in their land as straw is trampled down in manure. They will stretch out their hands in it, as swimmers stretch out their hands to swim. God will bring down their pride despite the cleverness of their hands. He will bring down your high fortified walls and lay them low; he will bring them down to the ground to the very dust." NIV translation
This period of time (Millennial Reign) will be a time of separating as well as uniting. The NIV translation is not as good with this passage as it gives the impression that the Moabites are swimming but that is not really accurate. The passage speaks of the hand of God parting the Moabites from His people much like a swimmer parts the water with an open hand. So, why is God parting the Moabites and who do they represent? We see the answer to the question of why in Deuteronomy 23 as God declared that they would be excluded from the assembly of His people. This was because of the fact that they had attempted to hire Balaam to curse God's people. Here, they are representative of all of the people of the earth that are enemies of Jesus Christ and His people. Who are the enemies of Jesus Christ? All of those who deny the fact that He is the Son of God who takes away the sin of the world. Those who have placed their trust in Jesus Christ will be united with fellow believers in celebration. Meanwhile, those that reject Him will be prepared for the final judgment which is separation and Hell.