The heart is as a King. And the armies are as servants and helpers. The armies visible to the eye, include, the hand/foot/leg/ear/eye/tongue etc. These were created with a disposition to obey the heart, and not to rebel against it.
Thus note: if the heart is pure, then it will command the limbs to do pure actions.
These things are related to preservation of the body.
And so the heart also needs this vehicle to gain knowledge, again with internal and external aspects.