Upper trigram
☷
Earth · Kun
Receptive yielding.
FamilyMother
ElementEarth
Hexagram 7 of 64
☷☵ The Army
Organised effort under clear leadership.
Lower trigram
☵
Water · Kan
Danger and depth.
FamilyMiddle son
ElementWater
The image
Earth above, Water below.
Earth over Water: receptive yielding meeting danger and depth.
That combination is the whole meaning of hexagram 7. Nothing about it is arbitrary — change either trigram and you get a different hexagram with a different reading, which is why the 64 form a system rather than a list.