A good article about 401k benefits. Most notably, a 401k plan offers the following benefits:

tax savings (the account is funded through pre-tax payroll deductions);
employer match incentives (free money that immediately boosts your return);
portability (can transfer the account to another employer or a rollover IRA); and
loan and hardship withdrawals (permits acces to money).

These aren’t all of the benefits of a 401k, but funding an account with pre-tax payroll deductions and enjoying tax free growth until withdrawal is good enough on its own!