At the risk of over-simplification, there are broadly two approaches to assessing the moral worth of an action: consequentialism and deontology. The first approach, also known as utilitarianism, judges actions by their consequences. It holds that if my action saves a thousand lives and harms no-one it is a good act, even if my act was in fact a theft. To some extent at least, the means justify the ends. The second approach judges an act by the character of the behaviour itself, so my act of theft may still be a bad act even if its consequences were overwhelmingly beneficial.
