N.T. Wright in his magnum opus The Resurrection of the Son of God discusses the different ways in which history is defined (12-14). Among the five senses of history, Wright argues that among scholars whatever-it-was-that-happened (referring to the resurrection) was “extremely significant,” though at the same time they argue that “we cannot know what ‘it’ is.”
The quest of historical research is to examine and report on an event, which is universally claimed as significant, but universally claimed–among unbelieving scholars–to not be clearly defined.
Paul, in I Corinthians 15, does not waste time with the debate over the significance and definition, but rather that it is, and what it means.