In a classical sense, particularly with capitalist economists such as Adam Smith, government was largely seen to only have to provide a judicial system (keep law and order), organise a military for defence and thirdly to provide public works or infrastructure (eg. roads) which the private sector cannot.
Your question is very subjective, as, depending on your political orientation, you could receive a wide variety of answers with this. Throughout history there has been struggles for a more socialist system of government whereby the government has more of a purpose in the economy.
I would stick with the first paragraph I wrote as your answer as it was the quintessential role of most governments up until the neoclassical age of economics in the 1800's.
Hope I helped and please rate my answer :)
