HaShem commands the Jewish people in this parashah: an eternal flame must always be kept burning on the altar, it must never be extinguished.
The fire on the altar where the sacrifices were offered always had to be lit.
In the Beit HaMikdash, the Holy Temple, there was a room where burning coals were kept to relight the Altar fire when necessary.
This mitzvah has a special meaning for us today.
Every Jew is a small Beit HaMikdash. The fire on the altar represents love for God. Just as the fire in the Temple had to be constantly burning, so too in our hearts, which represent the altar in the physical Beit HaMikdash, love for God must always burn brightly.
Extracted from Please tell me what the Rebbe says.