For what sins can someone lose their portion in the World to Come?
Our Mishna teaches that “All Israel have a portion in the world to come”.
This promise is based on the words of the prophet Isaiah (60:21) that
declares that the Jewish people are G-D’s handiwork in which He takes pride.
Perhaps a better question is not whether or not one stands to lose ones
place in the world to come (G-D forbid) by sin (chet in Hebrew) but perhaps
do ones actions demonstrate that one is indeed G-D’s handiwork in which He
takes pride?
Our actions in this world do relate to what and who we will be in the world
to come – who knows what our potential portion could be in the world to come
and what part of that portion could be lost or gained by our actions in this
world.
As far as losing our portion in the world to come completely, the Ramban
(Maimonides) teaches that there are sins which cut us off us from the world
to come – He lists these in his work – Mishna Torah, Hilcot Teshuvah,3:6.
I will not list them here as they require some explanation but if you are
unable to look them up yourself I recommend you talk with your Rav or
someone who in your congregation who has the knowledge to review this
section with you.
I hope this helps