Because of the compounding of investment returns over time, you have the ability to grow your account tax free, over the long-term. You don’t have to pay taxes on the amount of income earned that you contribute into your 401k, so it is a way of shielding your income from taxes. Since you will most likely be making more money now, and paying more in taxes now, than when you retire, when you do begin to withdraw from your 401k, it will be taxed at the rates that your income bracket will be when you are earning much less, thus allowing you to pay less taxes on that money in the future than you would be paying on it today, if you didn’t invest in your 401k. So you get retirement savings, company matches, tax deferrals, and tax free earnings just by deducting a small percentage of your income each year.