Back on the question of whether hell is a double payment....
By the way, are we clear now about the doctrine of Union with Christ? All the "in Christ" passages? Rom 6; John 15; Eph 1; etc.? (For a pretty good treatment of the doctrine, read the pertinent sections of Calvinist W.G.T. Shedd whose 3 vol Dogmatic Theology is one of the classic Calvinistic systematics. Or for a quick devotional though theologically sensitive work, read the little book by Lewis Smedes, Union with Christ.)
Anyway, regarding the charge that hell would be double payment if Christ indeed (according to Scriptures) tasted death for every man...
We might disagree over whether or not union with Christ is automatic or conditioned on faith, but Arminianism is not logically inconsistent with itself on the double payment issue. Let me explain....
Whether you're Calvinist or Arminian, you must accept a two-fold aspect to Christ's payment. First, Christ died for a particular person's sin, and second, God unites that person to Christ so that the person can be said to be "in Christ." Both Calvinists and Arminians are agreed on this issue. You must have both aspects!
Where the dividing point is, is whether Union with Christ is automatic. I admit that this is the real issue of the debate.
But, if we assume momentarily that Union with Christ is not automatic, but is conditioned on faith, then it is entirely logical to say that Christ bore a person's sin debt on the cross, but that the unbeliever remains unforgiven on the basis that he was never united with Christ.
Again, I admit that we all may disagree on whether union with Christ is conditional, but, if it is, then there is no logical reason to conclude that universal atonement entails a double penalty. Arminianism is logically consistent with itself on this issue.
Therefore, Calvinists should focus their debate effort on whether union with Christ is conditioned upon faith. But the charge of double payment ends up as red herring fluff. The real issue is whether union with Christ is by faith.
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(For further scholarly analysis of this issue, if anyone is interested, I would point to an article written by 4-point Calvinist Lewis Sperry Chafer, and reprinted back in the 1980s in Theology Today.)