The problem with metaphor in ritual is that it won't work for everyone. During grounding meditations involving visualizing roots reaching deep into the center of the earth, someone (me) might be distracted by imagining roots meeting red-hot magma. During rituals using a fall harvest theme, someone (me) might be distracted thinking about how nature is planting, not harvesting.
I've disguised more than one poorly thought-out concept with metaphor, so I understand the urge. They are also tempting to deploy as a substitute for true understanding of the ritual theme, or when deeper knowledge is hard to convey in the ritual context. Metaphors are best used cautiously and only when really necessary.
