Becoming a mother makes you the mother of all children. From now on each wounded, abandoned, frightened child is yours. You live in the suffering mothers of every race and creed and weep with them. You long to comfort all who are desolate.
There is a lot of truth in this but I have to disagree with the first sentence.
I don't believe that you need to be a mother to feel these feelings. I believe there is something which is changed within us when we are called to be mothers and it's this which joins you to the world of mothering.
Some of us are lucky enough to become mothers, some of us don't ever have the opportunity to bring up a child of our own. But no matter which it is, we are called to care so much that our hearts now live outside our bodies.
This is the definition of motherhood for me; it is the valuing of children beyond all else.