"Now if there is no resurrection, what will those do who are baptized for the dead? If the dead are not raised at all, why are people baptized for them?" NIV translation
It seems that there were some in the church who had fallen back into legalism. They thought that it was essential to be baptized in water to go to heaven and so made a way for the dead to sorta have a second chance. We notice that Paul did not condone this activity as he said "those" referring to the people that were doing it. He was simply making a point that even they believed in the resurrection or they would not have done this ritual.
"And as for us, why do we endanger ourselves every hour? I face death every day - yes, just as surely as I boast about you in Christ Jesus our Lord. If I fought wild beasts in Ephesus with no more than human hopes, what have I gained? If the dead are not raised, 'Let us eat and drink for tomorrow we die.'" NIV translation
Paul now turns to the persecution that he and the church faced. The resurrection is the heart of the gospel and he asks why anyone would endure for a lie. Without the resurrection, then, you might as well go along with the Epicureans and live it up here on the earth instead of endure the persecution for your faith.
"Do not be misled: 'Bad company corrupts good character.' Come back to your senses as you ought, and stop sinning; for there are some who are ignorant of God - I say this to your shame." NIV translation
Paul quotes from a Greek comedy by the poet Menander which the Corinthians would have been familiar with. Basically, he says that, if they continue to hang with those who are denying the resurrection, they will be lead astray. He goes on to say that they do not know God and so it is expected for them to act that way but, as Christians, the believers knew better.
"But someone will ask, 'How are the dead raised? With what kind of body will they come?' How foolish! What you sow does not come to life unless it dies." NIV translation
Now, Paul shifts the focus from the truth that the resurrection happens to what it looks like. He begins to explain by using the example of planting crops which was something that everyone back then could understand. He reminds them of the fact that, in order to have a crop, a seed must be buried in the ground.