I see that you've tagged this with Amergov and so I assume you are talking about the difference in what the role of the government would be in these two scenarios. If so, the answer is that providing universal health care would involve the government to a much greater degree in administering the health care system.
If the government sets up a system of universal health care, it will essentially be in charge of providing health care to the public. This would be similar to England's system. In such a system, the government would be deeply involved in all aspects of the health care system. Government agencies, for example, would probably have to set up rules for how much various people (doctors, nurses, receptionists, technicians) would be paid for their services.
By contrast, if "all" the government was doing was providing insurance, it would be much less involved in the day-to-day operations of the system. The government would pay for health care and presumably have a say in what kind of health care people could get and how much it would cost just as insurance companies do now. But outside of that, the government would not be involved in telling health care providers how to run their businesses. This would mean that the government would have to do much less administration if all it did was provide insurance.