ברוך אתה ה’ בונה ירושלים
BLESSED ARE YOU HASHEM, BUILDER OF YERUSHALAYIM
We give thanks now for this future kindness of Hashem, because when it is rebuilt it will already be too late to thank, for no longer will we have the Free-Will to choose to thank Hashem for His kindliness. Rather, we thank Hashem now, for His promise is certain to be fulfilled and we can trust in Him and we can thank Him today as if He has already returned to dwell among us in the midst of Yerushalayim.