Musar for Yevamot 127:2

This is the reason that G–d is perceived of as desiring the prayers of the righteous, since the service of G–d by means of prayer is a need that G–d feels, as we have mentioned on numerous occasions. The above is true only when the prayers are offered up in the Holy Land, a region from which the prayers ascend ever higher, something that cannot occur in the Diaspora in which the קליפות predominate and interfere. Prayers offered חוץ לארץ are as if dressed in the air of impurity, and it would be presumptuous to say that G–d longs for such prayers. Even in חוץ לארץ, however, the gates of tears subdue the forces of Lilith so that prayers offered in such circumstances are acceptable to G–d. The main difference between such prayers and identical prayers offered within the boundaries of ארץ ישראל is that the latter are something G–d has expressly desired. When the Torah speaks about וראית בשביה, the message is that while we are in exile, שביה, G–d does not desire that we worship Him in joy because we have not been found worthy to live in our homeland.

As long as Israel was in its own land, G–d yearned for our prayers, and that is why the patriarchs were people whose prayers are mentioned and from whom we learn the importance and efficacy of prayer. G–d even withheld basic needs such as children from them in order to "provoke" them into prayer. All this was true only as long as we lived in the land of Israel, a land which is under G–d's constant direct supervision. Since the other countries are supervised by G–d's שרים, angels appointed to look after the needs of the respective Gentile nations, why would G–d be interested in our prayers. Would they not become mixed in with alien elements, i.e. the respective שר supervising the nations that the Jews live in whose prayers are sent heavenwards? This is why the advice to the Jewish people while in exile is to send their prayers via ארץ ישראל, from there to Jerusalem; from there to the site of the former Sanctuary; from there to the site of the former Holy of Holies, the Inner Sanctum. From there the prayers are dispatched to שער השמים, as our sages have described this process. ...