Making sense of a Chazal

This morning I heard a speech that referred to the Sages' explanation for the fact that the Immahos [Matriarchs] were akaros [barren] as "Hakdosh Baruch Hu mithave letfilathan shel tzadikim" [G-d desires the prayers of the righteous]. It struck me that this hardly sounds comforting. On the contrary, it sounds like G-d, who actually lacks and, therefore, needs or should desire nothing deliberately withholds what people want just to make them jump through the hoops, so to speak. It sounds like a sadistic game. That's my kashe [problem or question].

So I thought about how this can be explained, especially given the context of the barren state of the Matriarchs. Think about this: a Matriarch by definition has to become a mother. That is her destined role. And the Immahos, who were all prophetesses, recognized what role was intended for them. And herein lies the answer to the kashe. Even when something is clearly seen as one's destiny, that does not mean it can be taken for granted. Thus the Immahos had to have children to fulfill their roles as intended. But they still had to work for the priviliege of having children. Even something that must happen, as it is central to the Divine plan, requires the individual to do her part. She cannot just sit back and say, "Well, if my role is to be one of the Matriarchs, then I am bound to have children, so there is no need to worry about it." It is not that G-d needs the prayers, for He needs nothing. It is for the righteous to get the opportunity to work through their prayers.