In the Zohar, Parshas Beshalach, we learn how important it is to learn after Chatzos (midnight), before Alos HaShachar (first rays of the sun, still dark). It says there that one who wakes up and joins together the night and day through davening to Hashem accomplishes a huge unification of the Feminine and Masculine aspects of Hashem, since the night corresponds to Din (Judgement) and Malchus which is Feminine, and the day corresponds to Chesed which is Masculine.
In Sefer Shaarei Kedusha from R’ Chaim Vital zy’a he brings this as one of the yesodos of becoming an eved Hashem (servant of God) and attaining Ruach HaKodesh. The reason for this is clear. The entire path of Kabbalah is about attaining balance, just like the Rambam writes that the main thing is to attain the middle path. The place of balance is Tiferes, that is, between the sefiros of Chesed and Gevurah. Through waking up while it is still night-time according to halacha and engaging in Torah study, specifically Torah Sh’Baal’Peh according to R’ Chaim Vital, we bring about harmony in our own personal sphere through unifying our heart and mind with utilizing our will to wake up and serve Hashem, along with the higher unifications which lead to hamtokas hadinim (sweetening judgements) and the geulah yechidis (personal geulah) and the Geulah Shleima.
Yismach Lev 