A "higher calling" usually means you try to do what "the higher Power" tells you to do....meaning you do what God tells you, and you act on His behalf. Your "calling" or your purpose in life is to obey God.

If you have a higher calling, you are going to do something that is more noble or more beneficial to mankind that either what your are doing now or what you could have done. If somebody gives up a regular job to do relief work in disaster-stricken countries, we would say that he had a higher calling.

it means having a higher level of job position