Mary was living her normal life, one shaped by her genes, culture, family, experiences etc, but was living her life in a way that must have resonated with an obedience to God, and with a character that reflected His character. That meant that when Gabriel appeared to her, what happened wasn’t a new and sudden calling on her life, it was a moment that sparked into life the fruit of her primary calling.
When I read Luke 11:27-28 it helped to clarify my thoughts about this. Jesus is teaching to a growing crowd, and Luke writes:
As he said these things a woman in the crowd spoke out to him, "Blessed is the womb that bore you and the breasts at which you nursed!" But he replied, "Blessed rather are those who hear the word of God and obey it!"
I love the way that Jesus underlines Mary's primary calling - to hear the word of God and obey it - without dismissing the reality of what this meant for Mary. She became Jesus' mother precisely because she was obedient in response to God what God asked of her, and being Jesus' mother was an important thing; just not the most important thing. Jesus words help us to understand what our priorities should be.
The act of calling into being is one of creation. When God creates us, He calls us. The very fact that we are alive, means we are called by God, and He is more interested in who we are becoming, how our character is developing than in what we do. Of course what we do is still important, but how we are doing it is more so. Perhaps then as we seek to grow as disciples walking alongside one another, one of the best questions we can be asking each other is "What is God saying to you at the moment? And how are you responding to that?" As we do this we can help each other grow in our primary calling of hearing and obeying God, because we all need help to do this.