It’s rare for an entire class to comprehend a new concept the first time it’s explained. That’s why teachers review.

And when the concept is essential to understanding not only a single day’s lesson but also a considerable chunk of the entire course, they’ll review and review and review — sometimes until the super smart students want to scream, “Enough already. We get it.”

But sometimes teachers need to bore the bright kids to buy the others time to get on board.

This column was created in a similar vein because there’s one thing that all readers should do somehow, someway. One thing that can augment a healthy lifestyle in so many ways.

Lift weights.

What follows, however, is not how to do this oh-so beneficial exercise but why.

That’s my job in this new world of technology: to provide the “why” to sell you — if you haven’t already been sold — on lifting weights.

Once you buy into that notion, you can easily find video online that clearly and correctly shows how to do each and every weight lifting movement that you choose to do. So let’s consider why (or more correctly “the whys”) weight lifting should constitute a considerable chunk of your week’s exercise.

You could easily cite a half dozen, but the why that clearly has the broadest implication is that weight lifting trumps aerobic exercise if you diet with the goal of creating permanent weight loss. That’s true even though aerobic exercise generally burns more calories and — irony of ironies — leads initially to greater weight loss.

But all weight loss is not the same when you clearly need to lose some. In that case, the only truly healthy weight loss is a loss of body fat.

While the loss of muscle mass may not adversely affect your overall health immediately, it increases the odds of the adverse occurring years later. Moreover, a significant loss of muscle mass while dieting makes keeping the lost weight from coming back borderline impossible.

Muscle, you see, needs a fair amount of calories each day to sustain itself. Fat does not.

So the 160-pound, middle-aged female who follows a 1000-to-1200-calories-a-day diet, runs three times a week but eschews lifting weights, and loses 20 pounds in two months, will not lose 20 pounds of fat.

She will lose some muscle not only because muscle requires calories, but also because we evolved from cavemen — and cavemen often went for days without food.

As a result, their bodies instinctively learned to hoard fat to avoid starvation. And that’s exactly what that female’s body does when it receives about half the calories it’s accustomed to.

In the best-case scenario, this lady’s 20-pound weight loss is a 15-pound loss of fat and five-pound loss of muscle mass. In the worst, it’s 10 and 10.

Either way, to maintain her new weight of 140 pounds, she’ll need to eat fewer calories (up to 500 fewer) than if she would’ve dropped the weight slowly and with the aid of weight lifting.

That’s because every pound of muscle in your body needs about 50 calories a day.

If this 160-pound female would’ve reduced her caloric intake by 250 calories per day instead of 1000 and lifted three times a week, her total weight loss in two months might total only five pounds — according to the bathroom scale.

But she would’ve lost eight pounds of body fat and added three pounds of muscle in the process.

Now she weighs 155, but looks as if she’s lost more, a trick on the eyes created by the fact that one pound of fat has 18 percent more volume than one pound of muscle. So if she follows the more moderate weight-loss pattern and doubles her weight loss to 10 pounds, it will look as if she lost closer to 15 or even 20 pounds.

Better still, losing the weight that way greatly increases the odds of keeping the lost weight lost.

Why? That six pounds of muscle she added requires about 300 calories a day to sustain itself. That’s 300 more calories she can eat each day without regaining weight when compared to losing the greater amount of weight without weight lifting.

Additionally, the weight lifting will improve her bone strength, resting heart rate and blood pressure readings, cardiovascular health, posture, sleep, mood and energy levels, her agility and mobility, and reduce the chance of inflammation occurring in the body, as well as the chance of dying prematurely by 25 percent.

Explained that way, there’s a good chance that even the slow learners in any class would fully understand why weight lifting makes such good sense — and is an absolute necessity for those who want to lose weight, keep that lost weight from returning, and promote overall health.