A few weeks back I as reading Isaiah on the train in the morning and I read the source of Paul's quotation in 1 Corinthians 15:32, in Isaiah 22. The traditional interpretation that I've heard preached is that if there is no resurrection then we may as well party up because there's no hope for anything beyond this life. This is all we have. I'm not so sure that this is an adequate interpretation and reading the context of Isaiah 22 gave me a little different picture.
8 The Lord stripped away the defenses of Judah,When we situate the quotation in its original context, yes, the residents of Jerusalem are partying up because they have no hope. But that is what they're judged for. In fact I think you could even call it the last straw.
and you looked in that day
to the weapons in the Palace of the Forest.
9 You saw that the walls of the City of David
were broken through in many places;
you stored up water
in the Lower Pool.
10 You counted the buildings in Jerusalem
and tore down houses to strengthen the wall.
11 You built a reservoir between the two walls
for the water of the Old Pool,
but you did not look to the One who made it,
or have regard for the One who planned it long ago.
12 The Lord, the LORD Almighty,
called you on that day
to weep and to wail,
to tear out your hair and put on sackcloth.
13 But see, there is joy and revelry,
slaughtering of cattle and killing of sheep,
eating of meat and drinking of wine!
“Let us eat and drink,” you say,
“for tomorrow we die!”
14 The LORD Almighty has revealed this in my hearing: “Till your dying day this sin will not be atoned for,” says the Lord, the LORD Almighty. (NIV)
When you read the book of Judges (and elsewhere in the OT) you see the same pattern repeated: the people sin, God sends a foreign nation to judge them, the people cry out in mourning and repentance, and God saves them. In Isaiah, as well, the people sin, God brings them to the brink of destruction, but rather than turn, they party on. Their eating and drinking becomes the last straw, the, 'sin that will not be atoned for' (Is. 22:14).
I want to suggest that perhaps Paul is bringing along with him the entire context of the Isaiah passage when he quotes Is. 22:13. If the dead are not raised then Paul is misrepresenting God. God had not vindicated Jesus and will not vindicate his followers (though from a different period than Isaiah, this would be akin to the Jews trusting in Egypt to save them from Babylon). Under that scenario, Paul should have realized that the opposition he was receiving was opposition from God. God was trying to stop his preaching, but his continual pressing on in his sinful activity meant that judgment was coming and Paul's sin could not be atoned for. I think that this explanation may make it clear why Paul chooses to narrate his own trials immediately preceding the Isaiah citation. If the punishment was from God then Paul has abandoned the God of Abraham by preaching Jesus.
I hope that makes clear that the quoted phrase is not Paul's actual suggestion to the Corinthians. Rather it's used as a catchphrase to bring to mind the wider context of Isaiah 22. In this way Paul also turns the tables on the Corinthians who did not believe in the resurrection. In fact, Paul wasn't mistaken, and his trials were not God's punishment intended to bring him to repentance. Rather it was the Corinthians who didn't believe in the resurrection and had fallen into licentious living (here I'm in line with Hays and Fitzmyer) who were the true enemies of God and were in danger of falling into a state from which their sin could not be atoned for.