The details were still unclear. His answer told Mary who rather than how and refocused her attention on the central task of trusting God. Perhaps the details were left out to prevent us from an immoral comparison with mythology. Crude stories about gods falling in love with women were popular. So God left the details unclear, but not the promise.
Spiritual life requires both faith and flexibility.
Often I would like to know the next step, but God's call to me, like Mary, is to trust and wait and obey as he makes the path clear. We are called to trust him. Mary's last word is better than her first. Thirty-three years later, her son would follow her example. Fifteen years ago, I waited for an answer.