The ZOHAR CHADASH (Shir ha'Shirim, p. 74) states that there are 600,000 letters in the Sefer Torah which correspond to the 600,000 souls of the twelve tribes of the Jewish people. Similarly, the MEGALEH AMUKOS (Va'etchanan #186:1) writes that the soul of every Jew stems from one of the 600,000 letters in the Torah. The name "Yisrael" itself can be viewed as an acronym for the words, "Yesh Shishim Ribo Otiyot La'Torah" ("there are sixty myriads (600,000) of letters in the Torah").
https://www.dafyomi.co.il/kidushin/insites/kd-dt-030.htm
עַד דְּסָלְקִין אַתְוָון, לְשִׁתִּין רִבּוֹא, כְּחוּשְׁבַּן שִׁבְטֵיהוֹן דְּיִשְׂרָאֵל, דְּאִינוּן תְּרֵיסַר, וְסָלְקִין לְשִׁתִּין רִבּוֹא. אוּף הָכֵי אַתְוָון, כַּד אִתְמָלוֹ סָלְקִין לְשִׁתִּין. אָלֶף בֵּית גִּימְל דָּלֶת הֵא וָו זָיִן חֵית טֵת יוּד כָּף לָמֶד מֶם נוּן סָמֶךְ עַיִן פֵּא צַדִּי קוּף רֵישׁ שִׁין תָּו. אִלֵּין אִינוּן סְלִיקוּ דְּאַתְוָון, לְשִׁיתִּין רִבּוֹא. בְּגִין לְמֶהֱוֵי שְׁלִימוּ בְּרָזָא דְּאַתְוָון, בְּשַׁיְיפֵי כּוּלְהוּ.
In the beginning, two thousand years before the heaven and the earth, seven things were created: the Torah written with black fire on white fire, and lying in the lap of God...
...ר"פ בשם רשב"ל התורה שנתן לו הקב"ה למשה נתנה לו אש לבנה חרותה באש שחורה היא אש מובללת באש חצובה מאש ונתונה מאש דכתיב (דברים ל״ג:ב׳) מימינו אש דת למו:
...Rebbi Pinchas taught in the name of Rabbi Shimon ben Lakish, The Torah which the Holy Blessed One gave to Moshe was white fire inscribed with black fire; fire mixed with fire, cleaved from fire and given from/by fire, as it is written: "From His right a fiery law to them"
...דאמר רב יהודה אמר רב כל אות שאין גויל מוקף לה מארבע רוחותיה פסולה
...Rav Yehuda says that Rav says: Any letter that is not encircled with blank parchment on all four of its sides, i.e., where its ink connects to the letter above it, below it, preceding it, or succeeding it, is unfit. When the mishna makes reference to one letter preventing fulfillment of the mitzva, it is referring to a letter that touches an adjacent letter.
Rav Abraham Isaac Kook, 1865–1935, first chief Ashkenazic rabbi of British Palestine
Black Ink on White Parchment
When we think about a Torah scroll, we usually only consider the letters themselves, written in black ink. Yet, the Talmud (Menachot 29a) rules that every letter in a Torah scroll must be completely surrounded by parchment. This requirement is called mukaf gevil. In other words, the white parchment around the letters is an integral part of the Torah; without it, the Torah scroll is disqualified. In fact, the white space is a higher form of Torah. It is analogous to the white fire of Sinai — a sublime, hidden Torah that cannot be read in the usual manner.
There is a delicate balance between black and white in the Torah. The shirot, the poetic portions in the Torah, are written in a special fashion, like a wall constructed from layers of black and white bricks. These poetic sections are the loftiest parts of the Torah. Consequently, they have more white space, as they contain a greater measure of the esoteric white fire. If a scribe were to write other sections of the Torah in this special layout, the Torah scroll would be rendered invalid. After the Torah was revealed and restricted to our limited world, it must be written with the appropriate ratio of black to white.
The Divine Call Before Revelation
The distinction between white and black fire also sheds light on God's call to Moses before speaking with him. The Voice summoning Moses to enter the tent was in fact the divine call from Sinai, an infinite call that never ceased (Deut. 5:19).…This Voice was not a revelation of Torah, but an overture to its revelation. It belonged to the esoteric white fire of Torah, before its constriction and revelation into the physical world.
This is the reason that Moses made the aleph of the divine call smaller. Since it belonged to the realm of white fire, the summons required an extra measure of white space over black ink. Superficially, Moses' miniature aleph humbly implies a diminished state of the revealed Torah of black fire, but on a deeper level, it reflects an increase in the esoteric Torah of white fire.
-Both passages by Rav Kook from Gold from the Land of Israel, pp. 179-181.
Rabbi Avi Weiss, 1944 to present, American Modern Orthodox
On the simplest level, black fire refers to the letters of Torah, the actual words, which are written in the scroll. The white refers to the spaces between the letters. Together the black letters and white spaces between them constitute the "whole" of the Torah.
On another level, the black fire represents the p'shat, the literal meaning of the text. The rabbis point to the importance of p'shat when stating "the text cannot be taken out of its literal meaning." The white fire, however, represents ideas that go beyond the p'shat. It refers to ideas that we bring into the text when we interact with it. This is called d'rash-interpretations, applications, and teachings that flow from the Torah. The d'rash are the messages we read between the lines.
On yet another level, the black letters represent thoughts which are intellectual in nature, whether p'shat or d'rash. The white spaces, on the other hand, represent that which goes beyond the world of the intellect. The black letters are limited, limiting and fixed. The white spaces catapult us into the realm of the limitless and the ever-changing, ever-growing. They are the story, the song, the silence. Sometimes I wonder which speaks more powerfully, the black, rationalistic letters or the white, mystical spaces between them.
-Excerpt from http://www.hir.org/a_weekly_gallery/8.16.02-weekly.html
