ORDINARY MAN CANNOT MAKE UP TO ALMIGHTY GOD FOR HIS SINS, EVER, IT TAKES GOD INCARNATE(JESUS) AND HE ALONE TO DO SO. THIS IS WHY JESUS IS OUR SAVIOR. 

The fact of the matter: Yes: because without God we would not be able to have eternal life from God suffering and God loved us that much that he gave his only begotten son to suffered for are sins so that some of us would have eternal life with God The Lord Jesus Christ our Lord and Savior in the new heaven and the new earth without sin. 

Actually, that sounds kind of grateful.  BTW, I'm also a grateful one.

Since Jesus already died for the sins of the world, Why suffer yourself for eternity

But that is the "Eternal Purpose."  Eph. 3:10-11.

No it is not selfish. Jesus paid the price so we wouldn’t have to. It’s what Jesus wanted to do for mankind.

Christians who really believe all that nonsense, must be mentally unbalanced, to put it mildly.

You're not even close to making sense.

We are eternally grateful for his sacrifice. He did it out of love for us and we accept it out of love.

John 15:13 KJV — Greater love hath no man than this, that a man lay down his life for his friends.

I actually do. Oath software won't let me share the video in my answer, but there's a video by Darkmatter2525 called "Is Christianity Moral?" In it, the angel Jeffery picks a random Christian, sends him back in time to the day of the crucifixion, and gives him an AK-47 with infinite ammunition. Not only doesn't the Christian use the AK-47 to rescue Jesus, he literally ends up shooting Jesus, thus changing that iconic moment in the bible where Thomas is told to put his hand in the hole in Jesus' skin.