In Parshas Vayakhel the Torah singles out the prohibition of lighting a fire on Shabbos from amongst all of the thirty nine melachos. Not kindling a flame is so essential to Shabbos observance that Shabbos begins with the lighting of candles and concludes with Havdala being accompanied by a beracha recited over the creation of fire. In addition to the prohibition of literally creating a fire, Chazal speak of a different kind of flame that may also not be lit on Shabbos; Chazal include the fire of anger in this Shabbos prohibition. Although not acceptable even during the week, there is a dimension of anger that is diametrically opposed to Shabbos.
How does anger contradict Shabbos? Chazal teach us that public Shabbos desecration is tantamount to idolatry. How so? Rashi explains that just as idolatry negates the truth of Hashem's existence, so too chilul Shabbos negates Hashem as the Creator of the world. Chazal equate one who gets angry with one who serves idols because in a state of anger a person makes himself into an avodah zarah. Chilul Shabbos and anger share the same attitudinal effect of being akin to avodah zarah. On Shabbos, therefore, one especially has to be careful not to become angry and thereby demonstrate his worship of himself.
Chazal instituted the mitzvah to light candles before Shabbos to enhance shalom bayis. Sitting in darkness inevitably leads to tension which will result in anger, thereby desecrating the essence of Shabbos, as explained above. The Gemara tells us that the Satan dances on Friday afternoon. It is a time when people may become tense as the last moments of Shabbos preparations occur, and therefore the yetzer harah of anger is present to potentially undermine Shabbos even as we prepare for the Shabbos.
The Mishna in Shabbos teaches us that one should instruct the members of ones household to complete the Shabbos preparations culminating with a reminder to light the Shabbos candles. Not surprisingly, we are instructed to give these instructions in a gentle tone. To insist on lighting Shabbos candles in an angry tone would undermine the shalom bayis the candles are coming to usher in. Such a tone of voice would enable the Satan to dance as proper Shabbos observance would give way to anger and ultimately a subtle form of idolatry.
As we begin and end our Shabbos from our Shabbos candles to our Havdala candle, it is fitting for us to focus on the power of fire in our lives. We can use this gift to bring light and warmth to those around us or become consumed with the fire of anger and dispute. May we learn the lesson of shalom bayis that our candles are teaching, and keep the Satan of anger far away from us.