You have one body and live inside it 24/7, therefore prioritising your health should be an obvious thing to do. Unfortunately few people care and severely underestimate its importance.
Treating your body right will provide you with a ton of energy, maximise your productivity and happiness, help prevent depression, promote longevity, and dramatically reduce (and in some cases eliminate) your risk for most diseases plaguing society.
As someone who has suffered from chronic disease, the difference between optimum and poor health is huge. Most people live their lives unaware of what health feels like because they've never experienced it.
It's the difference between night and day. If you're someone who genuinely wants to make the most of life, you should absolutely be taking your health seriously.
A common misconception is the purpose of health is for longevity. That's merely a bonus. The real benefit of health is to provide you with the energy and well-being required to make the most of life. Not later, but right now.
This means you need to eat well, exercise, sleep properly, meditate, and do whatever else is required to maintain your health.
When it comes to diet, however, few people are aware of the optimal human diet (this even includes most health conscious people and 'experts'). The amount of misinformation, industry 'science', corrupt health institutions, and douchebags trying to sell some fad diet has baffled society. Most people consume things believing they're healthy, when in fact they're proven to contribute to our leading causes of death and disease (such as meat and dairy).
Don't take my word for it. Go and read The China Study and take a look at Nutrition Facts. Although I know what I'm saying is true because of the evidence I've seen, blindly accepting what anyone says without looking into the science is a terrible habit that will lead you astray, therefore you shouldn't trust me. Do your own research, but ensure you don't cherry pick whatever 'evidence' suits you.
Adopting a healthy lifestyle is easily one of the best decisions I've ever made. Once it becomes a habit it honestly takes no effort. Don't wait until you're sick before you get your shit together. Even if you think you're healthy right now, you can guarantee you'll see a significant improvement in your quality of life if you adopted an optimal lifestyle.