ירמיהו, פרק ל״ו, פסוק כ״ב

During the cold ninth month of Kislev, the king seeks refuge from the harsh weather inside a specialized structure. This winter house was intentionally built to be completely sealed against the freezing winds, standing in direct contrast to summer homes that were designed to invite cooling breezes [רד״ק, מצודת דוד, ביאור שטיינזלץ].

To ward off the chill, a fire burns directly in front of the king [מצודת ציון]. The primary approach among commentators is that the fire is housed in a special receptacle used specifically by royalty and high officials. Although it appears as if the vessel itself is ablaze, it is actually the wood inside that is engulfed in flames, creating the illusion that the entire container is burning [רש״י, מצודת דוד, רד״ק].

Beyond this simple understanding, other traditions suggest that the focus is not on the container at all, but rather on the fuel. Some explain that the firewood was arranged to burn in a state of brotherhood, meaning the logs were placed so they would catch fire from one another and help each other burn steadily. Others suggest this refers to a specific type of wood known for its unique burning qualities [רש״י, רד״ק]. Alternatively, dried grasses may have been gathered and used as initial kindling to help spark the larger logs into a lasting blaze [מלבי״ם].