The Rambam (Rabbi Moshe Maimonides, Spain-Egypt, 1135-1204), in the third chapter of his Hilchot Teshuva, lists the groups of sinners who receive no share in the World to Come. Included in this category, as the Rambam discusses (Halacha 10; listen to audio for precise citation), are "Mahati'ei Ha'rabim," those who lead the public to sin. The Rambam emphasizes that a person who causes others to sin falls under this category regardless of the severity of the sin or sins in question. Even if he causes people merely to neglect a single command of the Torah, he is considered a "Mahati Et Ha'rabim" and loses his share in the World to Come. Furthermore, the Rambam notes, this status does not depend on the means through which one leads people to sin. The wicked King Menashe used force to cause his subjects to worship idols, threatening them with death; the founder of Christianity, by contrast, did not use force but verbally persuaded his followers to abandon the Torah. Both kinds of "Mahati'ei Ha'rabim" forfeit their share in the next world.
The next category of people who have no share in the World to Come is that of "Ha'poresh Mei'ha'sibur" those who isolate themselves from the Jewish people. The Rambam (Halacha 11; listen to audio for precise citation) stresses that a person can attain this status even without transgressing any particular sin. This status applies to a person who withdraws from Jewish communal life by not participating in their fast days or festive occasions, separating from the Jewish people during times of persecution, and generally not identifying himself as a Jew. Such a person has no share in the next world.
Finally, the Rambam defines the category of "Megaleh Panim Ba'Torah She'lo Ka'halacha," those who brazenly and defiantly transgress the Torah. Even if the transgression does not rank among the more severe violations of the Torah, the perpetrator loses his share in the World to Come if he displays a complete lack of respect and regard for the Torah's authority, and does not, as the Rambam writes, feel "shame" from the Torah. The Rambam speaks here of the Torah as a grand, powerful entity that must cause a person to feel humble and meek. A person who displays arrogance and shameless disregard towards the Torah even to just one of its laws or precepts is deemed a "Megaleh Panim Ba'Torah She'lo Ke'halacha" and has no share in the World to Come.
