Fear of God is the beginning of wisdom.
These days, we’re uncomfortable with the idea of “fearing” God.
With good reason.
For centuries, it has been presented as something that made us live in anxious anticipation of being punished for the slightest infraction — maybe even for no infraction at all.
We were always ducking possible thunderbolts.
“…No fear of the Name of God should have been instilled into the lives of people…It is cruel and damaging to life to spread fear in the name of God. God is life-eternal, purity and bliss…God is to be loved and not to be feared.” 
So why does Torah tell us to “fear God?”
The answer might be found, at least partly, in the meaning of the word “fear” in the Hebrew language and in its understanding and application within Jewish tradition.
The Hebrew word translated as “fear” — yirah/יראה — can also mean “awe.”
Years ago, I liked changing “fear” to “awe.” It was far easier to assimilate. Thus, it’s the “awe of God” that’s the beginning of wisdom.
Sounds good. But what does that mean?
For that matter, what is wisdom?
Put simply, “wisdom” means being able to act and live life “wisely” — knowing how to deal with people, knowing how to deal with the problems and issues that inevitably come up, knowing how to remain calm regardless of circumstances.
We all see that while a person can be put on the moon, far less “scientific” effort is placed on making life comfortable for everyone on earth. “Science” might produce “knowledge,” but not wisdom.
We see very intelligent people making very foolish choices.
Likewise, we see very informed, educated (often “successful”) people who conduct their lives with a complete lack of insight into their own behavior.
We see that business — especially as practiced in America — has become based on making the quickest and greatest possible profit, regardless of the effect on people, on the environment, on the world or even on the long-term economy of the country itself. It is profit without “wisdom.”
How do people allow themselves to do this?
By believing that there are no consequences of our actions; by denying any evidence of consequences (the denial by cigarette companies of the link between smoking and cancer, for example); by believing that consequences can somehow be “escaped,” especially with money — perhaps by buying property in some other country, or by buying off politicians or other government workers, and so on.
But Torah and TaNaCH teach much the opposite:
אָמַר נָבָל בְּלִבּוֹ, אֵין אֱלֹהִים
The fool says in his [or her] heart: “There’s no God.” 
Who is a “fool?” Not the person who is unable to understand. Instead, “fool” means the person who is being unwise.
The Divine always responds to what we do. As the Baal Shem Tov taught:
The Divine responds to our actions like our shadow responds to our own movements. 
The “fear of God,” then, means knowing that our actions have inevitable effects!
We need not fear an arbitrary response; we need not fear “bad luck.” “Fear of God” means being so saturated with this idea of inevitable effects that we wouldn’t even consider ignoring those effects when planning or deciding our actions. It means knowing that we can never escape the effects of what we do.
“Fear” has levels. The lower level is simply being certain of consequences for wrongdoing. The higher level is an avoidance of wrongdoing out of awe of God. In the lower level, we avoid wrongdoing in order to avoid its negative results on ourselves. In the higher level, we avoid wrongdoing in order to avoid marring in any way the joy and peace of our experience of God.
“Chazal [an acronym for ‘our sages, may they be remembered for the good’] generally delineate two categories of yirat Shamayim: the more pragmatic yirat ha’onesh (fear of punishment or retribution); and the more idealistic and ambitious yirat ha’romemut (awe).” 
Using the analogy of marriage: we might avoid any infidelity because we’re afraid of getting caught! But that’s hardly the best reason. It’s far greater to avoid infidelity because it would mar the love and security that the marriage partners share. Yet, both levels of “fear” can be useful tools to achieve the overall goal of a stable marriage.
It might even be possible to have “awe” without “fear.”
Einstein claimed to have felt a kind of “awe”:
“But the scientist is possessed by the sense of universal causation…His religious feeling takes the form of a rapturous amazement at the harmony of natural law, which reveals an intelligence of such superiority that, compared with it, all the systematic thinking and acting of human beings is an utterly insignificant reflection. This feeling is the guiding principle of his life and work…It is beyond question closely akin to that which has possessed the religious geniuses of all ages.” 
Yet, he equally claimed not to feel a “fear of God” based on that “awe”:
“I believe in Spinoza’s God, who reveals himself in the harmony of all that exists, not in a God who concerns himself with the fate and the doings of mankind.” 
Einstein was a person of immense intelligence; arguably the greatest scientific mind in all of history. Yet, from the Torah point of view, he was a person of limited wisdom.
So, both “levels” of yirah/יראה/”fear” are needed. Perhaps they’re not so much “levels” as “facets.”
“Wisdom,” therefore, means acting with awareness that our actions have inescapable effects, and with the intention that those effects be positive. Thus, both “fear” and “awe” are implied in “Fear of God is the beginning…”
The Talmud tells us that even so, we don’t sin unless a kind of madness enters us:
“One doesn’t sin unless a spirit of folly enters him [or her].” 
What is this “madness” that causes us to act contrary to all ethics and morality (psychopaths and sociopaths exempted)?
It is when we respond with thoughtless emotion alone — with greed, for example. Overwhelmed by emotion, we can disregard all of our own actual and potential mental reservations. Like the addict who needs a fix, and who will lie, steal and kill for it, even from their own family, we don’t, and can’t, withstand the onslaught of our own impulses.
As Rabbi Elhanan Wasserman wrote:
“If a beast of prey must be bound with an iron chain [to control it and limit the harm it could do], how many chains are needed to stop a terrible beast like man?
Now, when God created man, he certainly [also] created the chain to bind him so that he not destroy the world.
And what is this chain? It is the fear of God, which alone has the power to stop a man from being like a beast of prey. Other than it, no ruse in the world is capable of restraining a human being from wreaking harm. Even if one is a sage and philosopher like Aristotle, his wisdom [i.e. a wisdom based only on human reasoning and will power] will not protect him when his passion attacks him.” 
Just as God liberated us from slavery to the Egyptians, the “fear of God” — properly understood — can liberate us from slavery to our own impulses.
 Tehillim/Ps. 111:10
 Maharishi Mahesh Yogi; The Science of Being and the Art of Living; © 1966 by Maharishi Mahesh Yogi; p. 275-6
 Tehillim/Ps. 14:1
 Dvorkes, Rabbi Aryeh and Joshua; Chas. Wengrow, trans.; The Baal Shem Tov on Pirkey Avot; © 1974 by Rabbi Y.A. Dvorkes; p. 23
(this anecdotal teaching is from Rabbi Levi Yitzhak; Kedushat Ha-Levi)
The Besht is doing a drash/homiletic teaching on Ps. 121:5 — G-d is your shadow/ ה׳׳ צלך (usually translated “G-d is your shade…” i.e. your comfort or relief)
Elsewhere attributed specifically to Rabbi Bachya ibn Pakuda in Duties of the Heart 10:6. Other rabbinic authors use other terms to describe the grades of “fear…”
 Einstein, Albert; The Religiousness of Science: The World As I See It; The Citadel Press, Secaucus, NJ, © 1934, p.29
 Isaacson, Walter; Einstein: His Life and Universe. New York: Simon and Schuster, © 2008; pp. 388-389
[based on this, I’m not sure that Einstein fully and correctly understood Spinoza — but who does?]
 Sotah 3a