Fiat Mihi Secundum Verbum Tuum

The fidelity of the hour-hand of a clock which steadily traverses stroke by stroke the circle in which it is appointed to move. The mind, unceasingly moved by divine grace, turned insensibly to the new duty which presented itself in the order of God every hour. Such were the hidden springs of Mary's life, the most perfect example of simple and absolute self-abandonment to the will of God. 

The simple words, Fiat mihi secundum verbum tuum, ("Be it done unto me according to Thy word.") with which she was content to answer the angel, expressed all the mystic theology of the ancients. Then, as now, it was all reduced to the simplest and most absolute abandonment of the soul to the will of God under whatever form it manifested itself. 

This noble and exalted disposition, the basis of all Mary's spirituality, is brilliantly manifested in the words fiat mihi. Observe how perfectly they accord with those which our Lord would have ever on our lips and in our hearts: Fiat voluntas tua ("Thy will be done."). True, the duty required of Mary at that supreme moment was a glorious one for her. But all the splendor of that glory would have made no impression upon her if the divine will, alone capable of influencing her, had not arrested her attention. It was this divine will which guided her in everything.

Link (here) to Abandonment: or, Absolute Surrender To Divine Providence By Fr. Jean Pierre de Caussade, S.J.