Musar sur Les Nombres 24:3

The expression שער השמים, refers to the place from where our prayers ascend to heaven, a gate which, alas, is closed to us now; Rabbi Eleazar in Berachot 32, quotes Lamentations 3,8: גם כי אזעק ואשוע שתם תפלתי, "Though I cry out and and plead, He shuts out my prayers," as proof that the gates of prayer have been shut since the destruction of the Temple. He agrees, however, that the gates of tears have remained open. It is to be noted that the word שתם, "He shut out," is not spelled with the customary letter ס, but with the letter ש, which, by its opening to the top side suggests less than a total shut-out. We observe a similar use of the letter ש, when Bileam describes himself as שתם העין "open eyed" in Numbers 24,3 and 24,15. G–d will receive our prayers gladly in the rebuilt Temple. Even though the gate is closed while we are in exile, as long as we are not in Israel, our prayers are "detoured" from wherever they emanate via the land of Israel.