Mitzvah-candle versus Torah-light that never dims

בזוה"ק ע"פ אש תמיד תוקד דכתיב נר מצוה ותורה אור.

In the Zohar HaKadosh on the verse "A perpetual fire shall burn" (Vayikra 6:6): for it is written, "A mitzvah is a candle and the Torah is light" (Mishlei 6:23).

The Sefas Emes opens with the Zohar's reading of the "perpetual fire" on the Mizbe'ach in light of the pasuk that compares a mitzvah to a candle and the Torah to light.

ועבירה מכבה מצוה ולא תורה.

And an aveirah (sin) extinguishes a mitzvah, but not Torah.

Chazal teach (Sotah 21a) that a sin can snuff out the "candle" of a mitzvah, but it cannot extinguish the "light" of Torah. The Sefas Emes will explain why.

וכפי מה שאדם עושה המצוה בכוונה לבוא על ידי זה לדביקות הבורא ולקבל יראתו ית'.

And to the degree that a person performs the mitzvah with the intention of coming thereby to dveikus (cleaving) to the Creator and to receive His yiras Shomayim —

When a mitzvah is done not merely as an act but with the kavanah (intention) of using it to cleave to Hashem and to acquire yiras Shomayim, it takes on a higher quality.

עי"ז נקרא תורה שמקבל תועלת ע"י המצוה לתקן עצמו לשמים.

through this it is called "Torah," for he receives benefit through the mitzvah to rectify himself for Heaven.

A mitzvah performed with such inner intent rises to the level of "Torah-light," because the person draws lasting spiritual benefit from it, using it to perfect himself for Hashem.

ומצוה כזו אינה נכבית.

And such a mitzvah cannot be extinguished.

Once a mitzvah has been elevated to the status of Torah-light through inner intent, no sin can ever put it out.

כי מצוה הוא תיקון הרמ"ח איברים ולכן ע"י עבירה נתקלקל התיקון.

For a mitzvah is the rectification of the 248 limbs, and therefore through an aveirah the rectification is damaged.

A bare mitzvah corresponds to and repairs the 248 limbs of the body; since it operates on the physical plane, a sin — which also damages the limbs — can undo that repair and "extinguish" the candle.

אבל תורה הוא קבלת אור פנימי תוך איברי האדם אחר שנתקן ע"י המצות ולזה אין כביה עולמית:

But Torah is the receiving of an inner light within the limbs of a person after he has been rectified through the mitzvos, and for this there is no extinguishing ever.

Torah is a deeper, inner light absorbed into a person once his limbs have already been set right by the mitzvos. Because it dwells in the penimiyus rather than on the surface, it lies beyond the reach of sin and can never be put out.

Summary: "A mitzvah is a candle, the Torah is light." A sin can extinguish a plain mitzvah because a mitzvah rectifies the 248 physical limbs, the same plane a sin damages. But a mitzvah done with the kavanah of cleaving to Hashem rises to the level of Torah — an inner light absorbed into a person already rectified by mitzvos — and that inner light can never be extinguished.