However, Chauncy was a firm Bible-believing Christian and whilst he sadly came to doubt and then reject the classical doctrine of the Trinity we must stress that he did so because he believed it to be unbiblical (it was not uncommon in this period for Bible-based Christians to reject the Trinity as unbiblical).
Anyway, of interest here is that Chauncy became a universalist because he believed it to be the only view consistent with Scripture. In 1762 he preached a sermon entitled "All Nations Blessing Christ" which was the first hint at this new view. But the main work he wrote is a very scholarly (I'm not joking about the scholarly part) book published anonymously in 1784 entitled The Mystery hid from Ages and Generations, made manifest by the Gospel-Revelation: or, The Salvation of All Men: The Grand Thing aimed at in the scheme of God (they loved short and snappy titles in theose days)
The Salvation of all Men (1784) is a very impressive work - one of the more impressive works from the history of universalist theology. It provoked a book-length response from Jonathan Edwards himself entitled The Salvation of all Men Strictly Examined: and the endless punishment of those who die impenitent, argued and defended against the objections and reasoning of the late Rev Doctor Chauncy, of Boston, in his book entitled "The Salvation of all Men". See what I mean about snappy titles! At least you knew what the book was all about! It does what it says on the can. (for those who are interested you can download both books online. Here is Chauncy and here is Edwards).
Anyway, all I wanted to do was to draw attention to one of Chauncy's arguments regarding 1 Corinthians 15. The relevant text reads (in the ESV)
22 For as in Adam all die, so also in Christ shall all be made alive. 23 But each in his own order:
Christ the firstfruits,
then at his coming those who belong to Christ.
24 Then comes the end, when he delivers the kingdom to God the Father after destroying every rule and every authority and power.
25 For he must reign until he has put all his enemies under his feet. 26 The last enemy to be destroyed is death. 27 For "God has put all things in subjection under his feet." But when it says, "all things are put in subjection," it is plain that he is excepted who put all things in subjection under him. 28 When all things are subjected to him, then the Son himself will also be subjected to him who put all things in subjection under him, that God may be all in all.
Against the majority view Chauncy argues that Paul sees a temporal gap - perhaps a very long one - between the end of v. 23 and the start of v. 24 (p. 208). He reasons that Paul has in mind the Second Death when he speaks of 'death' in v. 26. Consequently, until the Second Death is destroyed (which is effected when all those condemned to Hell are redeemed) Christ has not defeated death.
Now I find CC's case unconvincing as an attempt to exegete what Paul meant (not least because his arguments, which I will not set out here, depend on interpreting Paul's meaning through the Book of Revelation).
However, there might be a theological argument from CC's reading of Paul that is suggestive. CC reasons that the grounds for thinking that death is an enemy would also apply to the Second Death - indeed more so. If death is an enemy of Christ that needs to be destroyed then the Second Death is more so. Both are divine punishments on sin that cause humans to fall short of God's ultimate intentions for them. If one was inclined to agree with such logoc then Paul's argument in 1 Cor 15 would require an extension beyond what Paul was talking about (i.e., the first death) so as to apply to the Second Death. In other words Paul has provided a theological argument that has an even bigger implication that he draws out explicitly (but one fully consistent with his universalist intro in 15:22).
Now CC also has a fall-back argument in case any readers have not been persuaded that Paul is speaking of the Second Death. It too is interesting. He points out that the kind of resurrection that would count (for Paul) as a defeat for the first death is not a mere restoration to life. Rather only a resurrection to glory and immortality would do the job. 1 Cor 15 makes that clear: only when 'the corruptable shall have put on incorruption' shall it come to pass that 'death is swallowed up in victory'. So until all have attained such a resurrection it cannot be the case that the first death has been fully defeated (and 1 Cor 15 requires that it is fully defeated).
Now this is an interesting argument - one I have never considered before. I am not sure that it would count as a straightforward exegesis of what Paul 'had in mind'. But it surely counts as a sensible reflection on the implications of Paul's reasoning. I don't think that Paul's concern in 1 Cor 15 was the salvation of all. I do believe that he asserted the salvation of all in 15:22 but his focus is on how that applies to believers. The damned don't appear in his scheme except in the gaps and by implication. But I think that CC helps us see how a theological reading of 1 Cor 15 that takes Paul's logic seriously can lead in universalist directions.