People use these terms almost interchangeably, but they are not synonymous.  Calling, Mission and Purpose are different for a reason.

Calling- Something specific God asks you to do for him. Sometimes it lasts a lifetime, sometimes three years. (Jesus was called to the Cross.)

Mission- Something God asks you to establish for him, like a school or a Church. (Paul was called to the Gentiles and established churches.) Jesus’ mission is to save the world. Peter was called to the Jews. Jeremiah was called to Prophecy, but his mission was to the exiles.

Purpose- is what you bring to your calling or mission that makes you particularly effective in them. It is a Core Competence (something you are perpetually great at) and Core Passion, (a condition or perpetual outcome you really care about).

When your purpose is employed within your calling and mission, your effectiveness and more importantly your Joy are both multiplied. You are useful, effective and get results.

THAT’S God’s Work in Progress