The ear of a person that heard My voice at Mount Sinai declare that ‘the Jewish People are My servants’ (Vayikra 25:55) — and not the servants of servants — and went and sold himself as a slave to another — deserves to be pierced.”
Rabban Yochanan ben Zakkai explained that we can learn this “gem of a teaching” (“k’min chomer” — see Rashi) when we learn the verse: “But if the Hebrew indentured servant says, ‘I love my master, my wife, and my children; I will not go free...’ his master shall bore his ear with an awl, and he shall serve him forever.” (Ex. 21:5-6)
In addition to this explanation for piercing his ear, Tosefot offers cites a Midrash that hints to the reason for using an awl — called “martzea” in the verse. The gematria of the word martzea is 400. Since the Jewish People were slaves in Egypt for 400 years and were redeemed by Hashem, this Jewish person who went and “acquired” a master for himself deserves to be pierced with a “martzea of 400”.
Kiddushin 22b
