Saying "Yes" to God
I would like to use the analogy of the a woman saying "yes" to a man to be his wife for the rest of his life.
The best basis for saying "yes" is pure love; love not in terms of need but only for love's sake. When a woman detects love not in terms of need, then her "yes" will have a meaning of a lifetime.
When we see our relationship with God as a need or a function, then we don't love God enough. That's why we can't commit ourselves to Him for life; instead we commit ourselves only when we are in need.
We need to know enough about God to commit ourselves to Him unlike Mary who knew, loved, adored, and served God. That's another reason we say "no", we don't know him enough. But if we do, then our journey with God really begins.
Knowing leads to dialogue and dialogue leads to shared vision. This leads to communion, of being one heart and one mind. The beloved becomes to resemble the lover. We become like God who loves us. And if God is "mercy and compassion", we too become "mercy and compassion".
Finally, Mary's fiat yields the fruit of love - the incarnation of the Son of God. Let our love bear fruit - Jesus Christ, in our children, neighbors and communities. That is the real fruit of saying "yes" to God - the birth of Jesus, leading to the transformation of the whole world in love.