Limited atonement and unlimited atonement. The Calvinist TULIP theology holds that atonement is limited only to the elect. The Arminianist counter-theology says that atonement is unlimited to all but only does any good, if you will, for the elect.
This problem is rather difficult to solve: we've always been taught that Christ died for all, but Scripture clearly states that Christ died for the elect. [Acts 20:28, for one reference.] This is one of the first times in this Calvarminianism series that I will use Scripture exclusively rather than Scripture combined with observations, because it's impossible to observe how Christ died in the modern world.
If atonement were unlimited, God would be unable to mete out justice on those who are not elect because their sins would be atoned for. [Calvinism 4, Arminianism 1.] If Christ died for all and the atonement of that death were unlimited, the blood-screen that Christ provided for the elect would protect the non-elect from the just punishment that they deserve: an eternity in Hell. Keep in mind that all of us deserve Hell, but that some of us were elected into salvation due to God's sovereignty. If atonement were unlimited, then God would not be able to be a just God and deal out justice to those who do not trust Him or believe in Him. Limited atonement limits Christ's atonement to the elect, which therefore enables God to measure justice on those who closed their hearts to Him.
Again, I am not perfect, I am not a theologian, I do not have a doctorate, and I do not claim to have all the answers. What I have just written makes sense now, but I will continue to learn more about this subject as my study of Scripture furthers itself. In the meantime, my status as a Calvarminianist is continuing to dwindle steadily.
Times appear to be changing: currently the score is Calvinism 4, Arminianism 1. To be continued, again.