Greetings...The image for the Number 18 was taken from the Higher Arcana of the Tarot.
The Tarot is a Universal Book of Archetypes. All Systems are interrelated and so it should be, if there is a Truth!
The 18th Card (The Moon - or La Lune) is associated with the astrological sign Pisces, two fish swimming in opposite directions. Do you see how the symbolism there does indeed speak of Spiritual/Material conflicts? Kind os a repeated theme, as it were.
In the Light...
A
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"The ALL is MIND; the Universe is Mental." *** The Kybalion