If the resurrection is the heart of the gospel how can any Christian deny life after death?

^12-19 Now if the rising of Christ from the dead is the very heart of our message, how can some of you deny that there is any resurrection? For if there is no such thing as the resurrection of the dead, then Christ was never raised. And if Christ was not raised then neither our preaching nor your faith has any meaning at all. Further it would mean that we are lying in our witness for God, for we have given our solemn testimony that he did raise up Christ—and that is utterly false if it should be true that the dead do not, in fact, rise again! For if the dead do not rise neither did Christ rise, and if Christ did not rise your faith is futile and your sins have never been forgiven. Moreover those who have died believing in Christ are utterly dead and gone. Truly, if our hope in Christ were limited to this life only we should, of all mankind be the most to be pitied!

But Christianity rests on a fact—Christ did rise

^20-23 But the glorious fact is that Christ did rise from the dead: he has become the very first to rise of all who sleep the sleep of death. As death entered the world through a man, so has rising from the dead come to us through a man! As members of a sinful race all men die; as members of the Christ of God all men shall be raised to life, each in his proper order, with Christ the very first and after him all who belong to him when he comes.

^24-27 Then, and not till then, authority and power, hands over the kingdom to God the Father. Christ’s reign will and must continue until every enemy has been conquered. The last enemy of all to be destroyed is death itself. The scripture says: ‘He has put all things under his feet’. But in the term “all things” it is quite obvious that God, who brings them all under subjection to Christ, is himself excepted.

²⁸ Nevertheless, when everything created has been made obedient to God, then shall the Son acknowledge himself subject to God the Father, who gave the Son power over all things. Thus, in the end, shall God be wholly and absolutely God.