Elul -To Learn the Entire Tanach

Rabbi Dovid Sears mentions an interesting Elul custom among Breslov hassidim:

Reb Nosson praises the custom of reading the entire TaNaKH during the days of Elul and Tishrei, finishing on Hoshanah Rabbah (See Otzar haYirah, Teshuvas haShanah, Elul).

Here is Reb Nosson in his own words:

בִּימֵי אֱלוּל וַעֲשֶׂרֶת יְמֵי תְּשׁוּבָה וְיָמִים נוֹרָאִים עַד הוֹשַׁעְנָא רַבָּא, צִוָּה לְכַמָּה אֲנָשִׁים לוֹמַר אָז כָּל סִפְרֵי תַּנַ"ךְ מִתְּחִלָּתָם וְעַד סוֹפָם, וְגַם הוּא בְּעַצְמוֹ נָהַג כָּךְ כַּמָּה פְּעָמִים. גַּם הָיָה גּוֹמֵר כַּמָּה סְפָרִים בַּיָּמִים הַלָּלוּ, וְאֵינִי זוֹכֵר לְבָאֲרָם הֵיטֵב

This is quite a hefty task to finish the entire Tanach in 40 days. Why should one learn Tanach at this time of year in particular?