The Republican's alleged purpose is to stop the government from using taxpayer money to fund abortions, which many taxpayers don't agree with. They point out that money, being fungible, can't be tracked to see what funding supports abortions and what part supports other operations. And they are correct on all of those points. But, anyone watching this debate can see that this is really about opposing abortion itself as a religious position and they are only going after funding because they can't find (at the moment, anyway) any other attack that might be workable. They are willing to shut down the government for period of time (which isn't all that bad in itself) and to do it even though the democrats and the media would go after them and be effective enough to put winning the 2016 presidential election in serious doubt. This social conservative side of the GOP has great strength and influence during the primaries. It is how they are able to keep themselves in power. (I'd be happy to see libertarian leaning Republicans shut down the government and to keep it shut down till a balance budget amendment (one with real teeth) was passed... if that could be done. That would be a fight worth having and if it could be done it would probably guarantee the GOP a win in 2016. But that's a different story.)
It is hard to know what is the more sickening, watching people engaging in phony pious obeisance to evangelics to get votes, or those who are actually so obessively tied to scripture that they'd give away an election for a futile gesture. One of the leading political advocates among the evangelical clergy (Reverend Jeffers?) appeared on the dais in Texas to endorse Trump! The political pathology grows so deep we need tall boots to wade about in that muck.
Here is a weird bit of political prognostication: It wouldn't surprise me if someone, say Gov. Bobby Jindal, who is a small government and religious right conservative, broke away and ran as an independent if the nomination goes to Trump. The argument would be that Trump is really a progressive just dressed up as conservative and lying to everyone. And it would be the small government social conservatives that would break away with him and give the election on a platter to Hillary or Biden. This is a bizarre election season, and one that is making me think the people might indeed get the government they deserve, and that is a really scary thought.