Rabbi Yehuda HaNasi ("the Prince"), the compiler of the Mishna, was renowned for his fabulous wealth and the luxuriant splendor of his household.
Word of his riches spread to other kings, and one day King Artaban of Persia heard about the great Jewish leader.
Now, Artaban was himself an extremely wealthy king with storehouses full of gold, silver and all manner of precious treasures. When he heard about Yehuda HaNasi's great wealth coupled with his brilliant mind, the Persian King decided that it would be to his credit to develop a friendship with the Jewish Sage. He thought at great length about how to approach the Nasi: he could send him a message; he could travel to meet him; or he could invite him to Persia. Finally, Artaban decided that since both were very wealthy men, he would take from his treasure house a beautiful and priceless gem and send it to the Nasi. Thus, he would give the Nasi a great compliment while also prompting him to return a gift of similar value, for Artaban was very curious about the extent of Rabbi Yehuda's wealth.
In order that the jewel be seen to its best advantage, Artaban had his finest artisans construct a golden box to house it. This box was a work of art in itself, fancy gold work laden with precious gems and lined in the finest plush fabric.
When the gift was completed and ready for presentation, all the courtiers, and even the king himself, were awed by its extravagant beauty. What could Rabbi Yehuda send in return that could begin to equal this fabulous gift?
Artaban readied the box, and with it he sent a letter explaining that he, Artaban, King of Persia, was sending this valuable gift to Rabbi Yehuda, the Nasi of Israel, as a token of his friendship and esteem. According to the accepted custom of rulers, it was understood that Rabbi Yehuda would respond in kind.
When the Persian messenger arrived, Rabbi Yehuda received him cordially, and when he examined the box and its contents he readily understood the value of the gift. But Rabbi Yehuda, unlike King Artaban, had amassed his great wealth, assembled his fabulous household, and even garbed himself in royal garments only for the honor of the royal House of Israel, to inspire the gentiles' respect for the Torah and its Sages. He had no personal benefit from all his wealth, indeed, at the end of his life he was able to say that he had experienced no personal pleasure from any of his riches.
Rabbi Yehuda considered carefully what to send to the Persian King in return. At last, he decided that he would send him a mezuza - one written on the most beautiful parchment, by the most meticulous scribe. To enclose it he had a beautiful case constructed of the finest precious materials.
Meanwhile, Artaban had been waiting impatiently for his messenger to bring him the reply and gift exchange of the Nasi. When he arrived at long last, the Persian hurriedly took the package, unwrapped it, and examined the contents. Instead of the priceless treasure he expected, he saw only a piece of parchment - a mezuza, something which could be easily bought in any marketplace. The King's rage and disappointment welled up inside him. He wasted no time sending Rabbi Yehuda a message berating him: "Why have you insulted me like this? I have sent you a gem so rare, it is priceless, while you have sent me a simple mezuza, a mere parchment which has the worth of one coin! Do you consider this to be an equal exchange?"
Rabbi Yehuda answered him: "I tell you that all of the treasures which lie in my storehouses plus all that you own together do not possess the value of that small scroll. For a mezuza is a commandment of the Torah, and the Torah of the King of the Universe is more precious than any treasure. In addition, you have sent me something which I must guard day and night, for fear that it might be stolen or lost. I, however, sent you a gift which will take care of you. When you attach it to the door of your home it will guard you whether you are asleep or awake, whether you are in your home, or traveling afar."
We do not know Artaban's reply, but Rabbi Yehuda HaNasi's words have come down to us as a reminder of the value of this precious mitzva.
