Our Gemara tells us that the Torah was originally written with black fire engraved in white fire. Rashi Deuteronomy (33:2) brings a similar teaching. What is the meaning of this?

The Maharal (Tiferes Yisroel 20) from what I can figure out seems to be saying that there are two kinds of potentialities in Torah. One is the active manifestation of G-d in his kindness and allowing things to exist through his power. This is how Avraham, who was known for Chessed kindness, fulfilled the entire Torah intuitively, as he did not seem to require every ritualary detail to experience the truths of the Torah, the white fire.  Then there is black fire, which is clear and without any apparent ambiguity.  This is the Torah of Yaakov, who was known for emes, truth without any grey area.  Thus the black fire and the white fire acknowledge the necessary aspects of Torah, the unambiguous and strict interpretation, and the white fire, which is more symbolic and open interpretation. 

I always had a habit of asking my children what meaning they could find in the various Midrashic stories. When my son Nesanel was six years old I asked him what did he think about the black fire and the white fire, and he said that it represented the evil inclination and the good inclination, yetzer hatov and yetzer hara, and that the Torah needs to encompass both aspects. It would seem that this is what the Shalah (Toldos Adam, end) seems to learn as peshat as well.

Never underestimate what a child will tell you when you ask him or her the right kind of question.