Republicans passed a bill to fund every part of government except for two minor Obamacare changes to which Democrats object.
Republicans say big business shouldn’t get a one-year delay from Obamacare requirements unless individuals get a delay, too. And, Republicans don’t want highly paid (on average double the private sector) senators, congressmen, and their staffs to get three-quarters of their health-care premiums paid by taxpayers over and above any normal Obamacare subsidies.
President Obama stated that these Republican changes wouldn’t stop Obamacare, so these aren’t the reason for the shutdown.
There is a partial government shutdown because President Obama believes he can win a political victory and bludgeon Republicans into dropping opposition to anything he wants.