“[I]t is not the source but the limitation of power which prevents it from being arbitrary.”

The "limitation: simply controls the damage that can be caused from the arbitrary use of power. The arbitrary use of power does not come from the source either. It comes from the power users choice to be arbitrary.

Arbitrary power can cause great damage to the economy, and the liberty of any free society. To limit it reduces the damage that can be inflicted

The “source”, at natural law (with a de jure common law application), prevents arbitrary power in and of itself. A “republican form of government” (Article IV Section 4 U.S. Constitution) is guaranteed at “the laws of nature and of nature’s God (Declaration of Independence) when each and every, any and all source of limiting power is recognized by/to the individual sovereign's nemo dat quod non haben = can not give that which is not had (as an individual sovereign, I do not possess the lawful authority or power to limit another's rights or liberty). Arbitrary power is rationalized and exercised by enslaved dupes’ allegiance and obedience to an inorganic / intangible / tyrannical phantasm (collective, democracy, religion, etc.). Solely limiting power to an existing arbitrary phantasm (government) without recognizing the true and lawful source of all authority and power is like closing the barn door after the horses have already got out.