It's a power play. Trump is throwing a fit because the Democrats won't agree to fund the wall and is holding the government and all its agencies in a shutdown until they agree to do so, thus making them look like the bad guys because of their continued refusal. According to something I saw recently it's basically putting everything at risk; many government employees including TSA and the Parks Service are working for no pay and thus having mass 'sick outs' where they just don't show up for work, making it harder for airports and those maintaining the National Parks to do their jobs, and many government programs like food stamps, disability and other aid will stop giving out whatever it is they offer if this isn't resolved soon. By holding the government in a shutdown Trump is effectively showing he holds all the power despite that not being how our government is supposed to work and people are going to die because of it.
