Why the servant's ear is pierced

טעם הנרצע אחר שש אוזן ששמעה עבדי הם כו'.

The reason the ear of the [Jewish servant] is pierced after six years: "the ear that heard 'they are My servants'…" (and yet went and acquired a master for himself).

Chazal teach that the eved Ivri who refuses to go free after six years has his ear bored through — the very ear that heard at Sinai that Bnei Yisrael are servants of Hashem, yet chose continued servitude to a human master.

ולא בשעת המכירה.

And [the ear is pierced] not at the time of the [original] sale.

The Sefas Emes notes the puzzle: the piercing comes only now, at the end of six years, and not back when the man first sold himself into servitude.

כי סבור הי' שיכול לקבל העבדות שלא ינתק עי"ז מעבדות של הקב"ה.

For [at first] he thought that he could accept the servitude without thereby being severed from his servitude to the Holy One.

When he first sold himself, he genuinely believed that serving a human master would not cut him off from his deeper avodah of serving Hashem.

ואחר שידע טעם עבדות בשר ודם שעי"ז פורק עול מ"ש.

But after he has tasted the nature of servitude to flesh and blood — that through it one casts off the yoke of Heaven (ol malchus Shomayim) —

Having now lived through six years of bondage to a human being, he has learned firsthand that such servitude does in fact erode one's submission to Hashem.

אין לו לומר אהבתי כו'.

— he has no right to say "I love [my master, my wife, my children; I will not go free]" (Shemos 21:5).

Now that he knows the truth about human servitude, his declaration that he "loves" it and wishes to remain is no longer excusable.

אף כי לעיני בשר נראה להקל חומר העבירה ע"י ההרגל שדש בה.

Even though to fleshly eyes it appears that the severity of the sin is lessened through the habit, since he has become accustomed to it (dash bah) —

Superficially one might think that long familiarity with a sin makes it lighter, since "once a person has trodden it down" it no longer disturbs him.

אבל באמת צריך להיות שונא יותר מי שיודע ומרגיש גודל החטא.

But in truth, one who knows and feels the magnitude of the sin ought to despise it all the more.

The opposite is true: the more deeply a person understands and senses how serious an aveirah is, the more he should recoil from it — not grow comfortable with it.

וגם כי המוכר עצמו מפני דוחקו אין עליו חטא רק אם אינו רוצה אח"כ לצאת אף שנתנה לו תורה מקום לצאת בשש.

And furthermore: one who sells himself because of his pressing poverty bears no sin — only if afterward he does not wish to go free, even though the Torah has given him an opening to leave after six years.

Selling oneself out of dire need is itself blameless. The fault lies only in refusing to depart once the Torah has provided a way out at the end of six years.

נראה כי התחלת המכירה לא הי' באמת מתוך הדוחק ולכן נענש על התחלת המכירה:

It appears that [in such a case] the original sale was not truly out of pressing need — and therefore he is punished for the original sale [as well].

His refusal to leave reveals retroactively that the first sale was not really driven by desperation but by an inclination toward servitude itself; hence the piercing of the ear punishes that original choice.

Summary: The eved Ivri's ear is pierced only after six years, not at the sale, because his refusal to go free shows what was hidden all along. At first he believed servitude to a master would not loosen his ol malchus Shomayim; having now tasted it and still chosen to stay, he reveals that even the original sale was not truly out of need. One who truly grasps the gravity of a sin should despise it more, not grow comfortable with it through habit.