Parshas Lech Lecha 5787
והיה ברכה ... (יב, ב)
On this posuk, Rashi says "יכול יהיו חותמין בכולן, ת"ל והיה ברכה, בך חותמין, ולא בהם".
The simple understanding of these words is that they refer to the first beracha of שמונה עשרה where we mention all three Avos, not just Avraham. In its closing one would've expected the same, but Chazal say that we only mention אברהם.
R' Shimon Shkop zt"l speaking in pre-WWII Europe, where the assimilation was ר"ל rampant, said the following pshat, al pi drush. Avraham was a ‘self-made’ Jewish man. He recognized Hashem of his own accord, as opposed to Yitzchak and Yaakov who had Avraham’s footsteps to follow. Logic would dictate that each following generation would be a strengthening link in our chain, but, alas, that was disproven by history, as waves of strong antithetical influences have infiltrated our circles. One would then fear that all is lost, but Hashem, ברוב חסדיו, promises Avraham ‘'בך חותמין." Just as you discovered Me through your own spiritual autonomy, so too, forever will your children always follow the path of return. We have all B"H, many a time, witnessed the rekindling of the sparks of neshamos making that comeback and returning to their roots.
He then adds another measure of chizuk by expounding on a posuk in Devarim which says, וטפכם אשר אמרתם לבז יהיה, המה יבאו שמה. The children that we thought,'לבז יהיה'would be lost forever,המה יבאו שמה ; they will return, and ultimately provide you with that much beseeched nachas.
Accordingly, this closing of מגן אברהם, recited by us thrice daily, contains an הבטחה, a promise given to Avraham Avinu for his progeny, that with Hashem's help there will soon be forthcoming a future shining day when each of us will declare with conviction, שמע ישראל ה' אלקינו ה' אחד.