Isa 63:3 I have trodden the winepress alone; and of the people there was none with me: for I will tread them in mine anger, and trample them in my fury; and their blood shall be sprinkled upon my garments, and I will stain all my raiment.
Rev 14:19 And the angel thrust in his sickle into the earth, and gathered the vine of the earth, and cast it into the great winepress of the wrath of God.
Rev 14:20 And the winepress was trodden without the city, and blood came out of the winepress, even unto the horse bridles, by the space of a thousand and six hundred furlongs.
Rev 19:15 And out of his mouth goeth a sharp sword, that with it he should smite the nations: and he shall rule them with a rod of iron: and he treadeth the winepress of the fierceness and wrath of Almighty God.
No one can read any of those verses above and not get a picture of how angry God gets. He's finally had it. He's fed up. The Holy loving eternally patient God finally reaches the point where He's not going to take it any more!
Picture all the defiant, rebellious, blasphemous humans who have shaken their fist in the face of God being tossed like grapes into a big wooden vat and then crushed so that their blood flows out like wine. Sounds horrible?
It is horrible. But, look at it this way for just a moment: sin requires blood. From the time Adam and Eve sinned ("thanks for nothing Grandpa!") and God killed animals to cloth them (cover them) to the moment Jesus died on the cross, blood has been sacrificed to cover sin.
However, for those that refuse to acknowledge the blood covering for their sin, and instead rebel and spit in God's face, they will have to shed their own blood and it will not be enough to cover their sin! When Jesus died and shed His blood, God said "it is finished" no more blood would be shed, no more blood could be shed that would be enough to cover sin. The ultimate Holy blood had been shed.
So when the Day of the Lord arrives, it's going to be a time of rejoicing and victory for saints and believers, but for the rest of the world it's going to be a crushing and bloody time of facing God's wrath.