A surprising number of people put off worrying about their nest eggs until the day comes where they realize they don't really have any plans. There are a million reasons why you need to start saving for retirement now, but below enough of them are explained to hopefully convince you of the importance of investing in your future.
Figure out how much you need to save for retirement--that number is exactly the reason why. If you retire at a nice young age, like sixty, you have to really plan on living to be about 100 unless you have a medical condition that proves otherwise. That is a lot of years to need income for. Figure out how much money you need to live on each year and multiple it by the number of years you'll possibly be retired. That is a big number. Don't be too scared--you can find a way to do this, but you need to start thinking about it as soon as you can and start saving for retirement.
Your current investments will have more time to earn you more money. If you put away a hundred dollars in a 401k when you're twenty years old and retire in your sixties, that's forty years that one hundred dollars was invested in various stocks, bonds, mutual funds, etc and earning you returns. That hundred dollars is suddenly a lot more money.
There will always be a reason not to invest--putting it off becomes a habit. If you're currently thinking you'll worry about saving later because right now you need to buy that new car, then tomorrow you're going to be saying you'll worry about saving later because right now you need to save to buy a house, and then pay off the house, and send your kids to college...and the list goes on. These are all worthy things and important parts of your life, but you need to budget for your retirement--another important part of your life--so that you'll have one.
The above reasons why you need to start saving for retirement summarize things, but there are even more. This is one of the most important things you can do for your life, don't ignore it.