Five reasons why there must be a day of judgment

1. Your conscience witnesses to it.
   
   Even when nobody else sees you, your conscience testifies, and gives you feelings of guilt. Your conscience is God's witness that you are seen, and that what you did matters.
   
   
2. God's character requires it.
   
   God is a God of perfect holiness. To expect him overlook evil done in his world is to expect him to not be God. Men are careful to monitor that company orders and laws of the land are being obeyed - do we think God is less than we are?
   
   
3. Because justice is not done in this life.
   
   If God's character requires justice, then there must be justice on some future day because we're all sure it isn't done in this life. Hitler "cheated justice" by committing suicide before he could be caught - but in fact he didn't, because this present age is not the age in which all the accounts are settled.
   
   
4. Christ's resurrection proves it.
   
   "And the times of this ignorance God overlooked at; but now commands all men every where to repent: Because he has appointed a day, in the which he will judge the world in righteousness by that man whom he has ordained; of which he has given assurance unto all men, in that he has raised him from the dead." - Acts 17:30-31. On the day you locate the tomb and body of Jesus, you may call into question God's judgment; until that day, you can know that God has already marked out the judge for you to know who he is.
    
   
5. God's love to his people requires it.
   
   God has chosen certain people. Those people are ignored, despised and rejected by this world which prefers to glorify its own values and praise its own politicians and celebrities. This has gone on from generation to generation. God is not such a God that this either pleases him or that he will be content to never do anything about it. They will be publicly vindicated.