大般涅槃經疏 1.34

1.34

次前後圍繞者，威儀也。或以三業恭敬機動，或以四門入空機動，或以四門入假機動，或以四門入中機動。

Next, 'surrounding [him] before and behind' refers to their deportment. It is either the stirring of capacity through the reverence of the three karmas, or the stirring of capacity to enter emptiness through the four gates, or the stirring of capacity to enter the provisional through the four gates, or the stirring of capacity to enter the middle through the four gates.