(2002/5763)
In the beginning of פרשת לך לך Hashem instructs אברהם to leave his birthplace to go to a land that Hashem will show him. In return for following this arduous task Hashem promises יהיה ברכה. The יהודי הקדוש מפשיסתא comments: what is the difference between הצלחה and ברכה? He answers that הצלחה results from a natural phenomenon, whereas ברכה results from a supernatural phenomenon. חוץ לארץ is unfortunate to have only הצלחה, events that could be explained by logic and reason, but ארץ ישראל is fortunate enough to have ברכה also, events that are above the restrictions of nature. This is the meaning of the פסוק (תהילים קכח :ה) יברכך ה' מציון, “It is from (ארץ ישראל) ציון that Hashem delivers to gift of ברכה.”
This is why Hashem said to אברהם, לך לך מארצך וממולדך... אל הארץ אשר אראך. In חוץ לארץ, אברהם could not merit to have children because he is so old. However in ארץ ישראל Hashem can give him the ברכה of בנים.