Sefer HaKuzari - Rabbi Yehudah HaLevi ( Shlomo Aviner 4 Vol.)

One of the most beloved Jewish philosophical works.
Written by Rabbi Yehudah HaLevi over a period of twenty years and completed in 1140, The Kuzari has enthralled generations of Jews and non-Jews alike with its
clear-cut presentation on Judaism, and its polemics against Greek philosophy,
Christianity, Islam, and Karaitism. Part historical novel, The Kuzari records a dialogue between Bulan, the eighth-century King of the Khazars (a powerful people occupying the region which is now southeast Russia between the Black and Caspian Seas), and a rabbi. The story is told that a righteous king was plagued by a recurring dream in which an angel told him 'Your intentions are desirable
to the Creator, but not your deeds.' This prompted him to summon a Greek
philosopher, a Christian, a Muslim, and a Jew to his palace to guide him on the
proper religious path. He was dissatisfied with each theologian until he heard what the rabbi had to say, and finally conceded that Judaism was the one true and correct religion. History records that Bulan and his entire kingdom then converted to Judaism. Never before in Jewish history had an entire nation of non-Jews embraced Judaism. The Kuzari describes the theological struggles of King Bulan and the convincing arguments of the rabbi which led to the mass conversion. Using this premise and the dialogue format as his vehicle, Rabbi Yehudah HaLevi succeeds in presenting, in a passionate and convincing fashion, some of the most important fundamentals of Judaism, including the different levels of creation, how God interacts with the physical world, and the sanctity
of the Sabbath and other holy days. As modern readers are drawn onto the
centuries-old debate, they will join the Khazar king in rediscovering the
beauty, truth, and wisdom of Judaism.