I'm quoting the original 152page strong Screenplay of Avatar:
Shafts of dawn light reach to the bottom of the grotto, lighting a single willow -- the MOTHER TREE. Ancient and gnarled, it grows in the center of the rock.
Its ROOTS spread down to the grotto floor, where they merge with the roots of the willows ringing the Well -- forming a braided mat resembling the surface of a brain.
Mo'at stands on the dais, leading them in a CHANT.
MO’AT (subtitled) Wise ancestors who live within Eywa, guide us. Give us a sign.