Destructively Diminished

The Gemara says מיום שחרב בית המקדש אין לו להקב"ה בעולמו אלא ארבע אמות של הלכה בלבד,[1] since the day the Beis Hamikdash was destroyed, Hashem has nothing in His world but the four Amos of Halacha. Why specifically four Amos?

The Gra[2] explains as follows: We are taught[3] that the Torah was written on a scroll of 20 by 20 Amos, which is 400 Amos. Sefarim[4] tell us that prior to the destruction of the Beis Hamikdash in the days of Hillel and Shamai there were 600 orders of Mishnayos. The elders of Beis Shamai and Beis Hillel saw the people’s hearts diminished due to the destruction and therefore only six orders of Mishnayos (ששה סדרי משנה) were arranged, leaving the rest behind (594). That is 1/100 of what it originally was. So there were 600 orders of Mishnayos when it was 400 Amos. Just as the Mishnayos is 1/100 what it was—from 600 to 6—so too 1/100 of 400 is 4 (Amos). This is the meaning in since the day the Beis Hamikdash was destroyed, Hashem has nothing in His world but the four Amos of Halacha. 

In the name of the Baal Shem Tov a different explanation is given: The symptom of the Beis Hamikdash being destroyed is that we believe Hashem can only be found in the four Amos of Halacha (Torah). However, the truth is אין עוד מלבדו, there is none other than Hashem and that in everything we can find godliness.