The spirit rising in a person cannot bind itself to the emotions and keep its light. That is the weariness sounding here through the mother, the soul's own longing: the developing self is warned against wedding the fearful, reactive feelings that belong to the land, to the flesh's own ground. To take a wife of Heth is to let the awakening spirit intermarry with dread and the churning moods, and once it does, the whole aim of the inner life comes to nothing.
What rises must stay unmixed. The spirit joined to fear is dragged back down into the body's alarms and loses the very thing that made it spirit. So the warning is simply this: the part of a person that is climbing toward the light must not fall in love with its own fears.
Daughters of Heth: the emotions and fear, the reactive moods of the flesh that the awakening spirit must not marry
Daughters of the land: the feelings born of the body's own ground, the terror and craving native to earthbound life