釋禪波羅蜜次第法門 3.28

3.28

若繫心地輪，此最在下，氣隨心下，則四大調和。亦以扶本修習不淨觀者，多從下起，因此繫心，或能發本。

If one ties the mind to the earth-wheel, this is the lowest; as the qi descends following the mind, the four elements then harmonize. It also assists one's original practice of the contemplation of impurity, which mostly arises from below; by tying the mind because of this, one may be able to arouse the original [practice].