Of the Divine commandments which is beyond man’s intellectual understanding, is the commandment of Brit Mila. This Mitzvah was first performed by our patriarch Avraham, with all his great difficulty at the age of 100 years and continued by his children for all generations, and became a sign of the covenant, the ultimate bond between Israel and their G-d.
The Kuzari king is amazed how the Jewish people throughout the ages have fulfilled this deed with the greatest effort and happiness and therefore as our Sages explained in the merit of this great Mitzvah performance the Jewish people continue to fulfill this commandment both with joy and under the most difficult situations.
During the course of history nations and religions have tried to imitate the Jewish people and have not been successful since their actions are only external and not related to their inner beings, even when cultures have decided to create a Sabbath day like the Jewish people they devoted their energies to idols and images and not to a G-dly creator.