When we [Americans] talk about the rule of law, we
assume that we’re talking about a law that promotes
freedom, that promotes justice, that promotes equality.
—U.S. Supreme Court Justice Anthony Kennedy

As Glenn Greenwald says in the video below, we have two, and only two, options:

A nation of men, or
A nation of laws.

Nothing could be more important to a civil society.

The principle of Rule of Law is intended to be a safeguard against arbitrary actions of the government authorities...The term Rule of Law does not provide any thing about how the laws are to be made, or anything specific like the Fundamental Rights or the Directive principles or equality etc. but it provides for two basic concepts that is Law must be obeyed by the people and that the law must be made in such a way that it is able to guide the behaviour of its subjects.

"The king himself ought to be subject to God and the law, because law makes him king."

The Rule of Law was founded with the Magna Carta, but the concept is far more important today. The entire concept of freedom starts with the Rule of Law.

Rule of Law is actually the very founding stone on which the platform of democracy stands. It is considered as the integral part of a democratic setup. The value of democracy lies in respecting the rights of others and the way they want to express themselves either by speech, writing, painting, drawing etc. And above all Rule of Law means nonarbitariness which can be ensured by guarenting freedom and one of such freedom is freedom of speech and expression.

It is for all these reasons and more that a two-tiered justice system, where the wealthy and powerful have a separate, privileged standard of justice, is totally incompatible with freedom, democracy, and the Rule of Law.

A two-tiered justice system is exactly what we have today, and everyone knows it.
To be fair, a two-tiered justice system is nothing new. Just ask blacks in the South during Jim Crow days. Or Chinese immigrants during the same era.
Discriminating against a minority is nothing new in any human society.
It's not healthy to society, but societies can tolerate a low level of injustice for a long period of time.

The difference today is scope. We are talking about discriminating against the vast majority.
Maybe 90% of the population. This is roughly akin to the two-tiered justice systems of feudal Europe.
This sort of societal paradigm is unstable, and can only be maintained by constant force.

I would like to offer the premise that what we have in this country is actually a three-tiered justice system.

The lowest level is for The Great Unwashed like you and me.

Les Miserables in real life

A homeless man robbed a Louisiana bank and took a $100 bill. After feeling remorseful, he surrendered to police the next day. The judge sentenced him to 15 years in prison.

Legal theft

State and local police seized $2.5 billion in cash from nearly 62,000 people without warrants or indictments between 2001 and 2014, an investigation by The Washington Post found. These agencies generally use the proceeds to pad their budget and buy new cars and other police equipment; in Texas, the money can even go straight into officers' pockets in the form of bonuses. Not surprisingly, police departments that have become heavily reliant on forfeiture fiercely oppose any efforts to curb the practice. They argue that forfeiture rules allow law-enforcement agencies to disrupt drug-trafficking operations. Many cases — more than 70 percent in Texas — aren't contested, which police say implies guilt. Attorney General Jeff Sessions insists forfeiture is justified, saying that "95 percent" of cases involve criminals who've "done nothing in their lives but sell dope."

Is that true?
The evidence suggests that it's not. People often can't try to retrieve seized assets because they don't have enough money to hire a lawyer for a long, grueling battle. The value of assets being seized, moreover, indicates that many forfeiture targets are hardly major drug kingpins. And abuses of the system are well documented. In 2014, cops at Cincinnati Northern Kentucky airport confiscated $11,000 from a student named Charles Clarke because they said his suitcases smelled of marijuana; the cash was his life savings, and it took him two years to recover the money. In 2012, police wrongly confiscated $17,550 from a restaurant owner in Virginia. By the time he recovered his money, 12 months later, his business had gone bust because he lacked capital.

Outright theft from the powerless by the state is the sign of a society in the late stages of decay.
Another sign is overcriminalization.

In 1998, an American Bar Association task force estimated that there were more than 3,000 federal criminal offenses scattered throughout the 50 titles of the U.S. Code.
Just six years later, a leading expert on overcriminalization, John S. Baker Jr., published a study estimating that the number exceeded 4,000. As the ABA task force reported, the body of federal criminal law is “so large . . . that there is no conveniently accessible, complete list of federal crimes.”
If “ignorance of the law is no excuse,” then every American citizen — literally, every single one — is ignorant and in peril, for nobody can know all the laws that govern their behavior.

Making virtually everything a crime is the logical next step when your objective is to keep people submissive while you rob them blind.

Above us is The Good and True.
They are subject to the law, but it's the law with kid's gloves.

Robert H. Richards IV was an unemployed heir living off his trust fund of Irenee du Pont, of the Du Pont Chemical Company.

Richards was initially indicted on two counts of second-degree child rape for raping his infant son and three year old daughter. If convicted of the charges, he would have faced a minimum ten year sentence...
When it came time for sentencing, Superior Court Judge Jan Jurden said Richards “will not fare well” in prison. Richards was given probation and rehabilitation instead. A confessed rapist basically avoided prison because the judge thought a wealthy man could not handle prison.

Samuel Curtis Johnson III is a billionaire from Wisconsin and heir to the SC Johnson cleaning supplies empire. Johnson was originally charged with felony sexual assault of a child for targeting his stepdaughter for three years.
Johnson confessed when confronted by the mother. He faced 40 years.

The charges had to be downgraded to a misdemeanor when the court held that the stepdaughter could not testify unless she and her mother released her medical records. Johnson’s lawyers wanted the records to see if the stepdaughter had reported the abuse to her therapist. They refused and the case fell apart without her testimony.
Samuel Curtis Johnson was sentenced to four months in jail, but will likely serve only sixty days.

Rich assholes like this are still subject to the law, but they can buy more justice. And if they have to go to prison, well there are conditions for that too.

Called "pay to stay," these programs allow offenders to pay anywhere from $82 to $155 a day and serve hard time in a clean, quiet cell, furnished with typical Oz fare like fluffy pillows, warm blankets, private TVs, a refrigerator, private phones, fucking board games, and chairs not made out of cold, depressing, ass-shattering concrete.

Then there is the top-tier. The Untouchables. They are simply above the law.
Goldman Sachs, need I say more?

Goldman Sachs is on a shopping spree. Last week, it spent $500 million to buy 12 percent of Riverstone Holdings, a private equity firm focused on energy investments. This is part of a $2 billion private equity strategy for the vampire squid. Through a couple of subsidiary funds, Goldman has already acquired stakes in private equity players Littlejohn & Co. and ArcLight Capital Partners, and Accel-KKR, a firm specializing in tech companies.
There’s only one problem with these investments: They’re supposed to be illegal under the Dodd-Frank Act. But “the law” is only as good as the men and women willing to enforce it, as Goldman Sachs has discovered to its delight.

When HSBC was caught knowingly laundering money for Mexican drug cartel and terrorist groups, Attorney General Eric Holder said, "I am concerned that the size of some of these institutions becomes so large that it does become difficult for us to prosecute them when we are hit with indications that if you do prosecute, if you do bring a criminal charge, it will have a negative impact on the national economy, perhaps even the world economy."

The ultimate of The Untouchables are in Washington D.C.
They not only can torture and assassinate people, even American citizens away from any battlefield, they can admit it on camera without shame or remorse, and without even denying that laws were broken.
That's truly the powers of Kings.

There are multiple problems that will all eventually arise from casting aside the Rule of Law.

1.) It's bad for the economy. Without trust in the Rule of Law, people are going to be more reluctant to make long-term investments, start businesses, etc. They could be financially crushed by the state, or a politically powerful client, at any time.
This makes the economy less dynamic, less innovative, fewer jobs are created, and everything slows down.

2.) People become aware of the unfairness and lose respect for the law and the society that tolerates it. Soon you start seeing what happens in third-world nations where so few people bother to vote that those elected have no legitimacy. The corruption at the top trickles down.

To make laws that man can not and will not obey, serves to bring all law into
contempt. It is very important in a republic, that the people should respect the
laws, for if we throw them to the winds, what becomes of civil government?
—Elizabeth Cady Stanton

3.) Eventually all faith in the state is lost. At that point only bribes and brute force gets things done, and both of those methods are extremely expensive. Empires cannot be built or maintained on bribes and brute force.
A good way of looking at it is comparing the Battle of Cannae with the Battle of Poitiers.

In 216 BC, Rome put 86,000 troops in the field against Hannibal, and lost roughly 75,000 killed and captured. They somehow managed to recreate an army after that disaster and eventually win the war.
In 1356 AD, France could only collect 11,000 troops to fight against England, and lost half of them, including the King himself. Immediately after the battle, French rulers experienced a general peasant revolt. The nation foundered and was forced to sue for peace.

Why the drastic differences, both in how many men could be raised to fight, and how society reacted to the defeat?
Simple: Rome in 216 BC was a republic, and moderately free. France, 1,550 years later was a corrupt, authoritarian monarchy, ruled by force. It's hard to get men to fight for things that aren't worth fighting for.