Q. Why do we preface each chapter of Pir’kei Avot with the statement, “All Israel have a place in the World to Come”?
A. This is a quotation from the Mishnah, from the beginning of Sanhedrin chapter 10. In Sanhedrin the context is that the courts have the power to sentence a criminal to death. The implied question is, does a person put to death by the court lose their place in the World to Come? The answer is that the promise of the afterlife remains so long as a person has not rejected basic Jewish beliefs.
Why this passage is borrowed for use before each chapter of Pir’kei Avot may be as an assurance that a non-intellectual who cannot carry out in-depth Talmudic study should not feel rejected so long as they devote time to easier subjects of study such as this. Another view is that living according to the wisdom of Pir’kei Avot gives a person a taste of the afterlife while they are still alive on earth.