This theme is very popular among Sufis: that although the heart is seemingly limited, if it would receive Divine attention then the whole universe-- even including the Creator of the universe-- can make a home within it. On this subject, for a bit of discussion see
Mir has several times versified the theme of the expansiveness of the heart. Then, there's this verse by Shah Niyaz Barelvi:
siine me;N qulzum ko le qa:tre kaa qa:trah rahaa
uf re samaa))ii tirii uu re samundar ke
chuur
[having taken a blood-ocean into the breast, hardly a drop remained
oh, your capacity! ah,
the atoms of the sea!]
On this there seems to be a slight influence of Maulana-e Rum's [Persian] verse (from the first daftar of the Masnavi):
'The drop that would become a traveler on the sea of oneness,
That drop makes captive all the
seven seas.'
Rumi has no equivalent to the insha'iyah style and the powerful image of the 'atoms of the sea' in Shah Niyaz Sahib's second line. But the Maulana has, in the sixth daftar [of the Masnavi], expanded upon this theme and given to his words an extraordinary sense of oneness and mysteriousness, such that (at least as far as the verse goes) Shah Niyaz and Mir have not reached it. God Most High says:
'I am not contained in the skies, nor in the emptiness of space,
Nor in intellects, nor in spirits.
I am contained in the believer's heart, like a guest,
Without
likeness, without attributes, without a condition,
So that that heart might mediate the highs and lows
And attain
kingship over them.'
Mir doesn't usually have that all-embracing command of Sufistic themes that Rumi does. But in image-making and in the immediacy of 'tumult-arousingness' Mir's side of the balance-scale usually outweighs Rumi's.
Thus in the present verse for the house of the heart to be very small, and then for there to be surprise as to how the whole universe has been contained in it, is a structure that makes an absolutely immediate effect. Then, with regard to ghar , the zila with jaa))e (meaning 'place') is very enjoyable. In
the idea of putting the face inside the collar and looking, and the image of a desolate wilderness/jungle, have given the verse a dastan-like or enchanted air.
Mir's verses noted below are devoid of those qualities. From the first divan [{361,4}]:
hai farsh ((arsh tak bhii qalb-e ;hazii;N kaa apne
is tang ghar me;N ham ne dekhii hai;N kyaa fa.zaa))e;N
[from the earth even/also to the empyrean belongs to my melancholy heart
in this narrow house, what spaces have we seen?!]