The Greatest Segulah

The Nefesh HaChaim, zt’l, famously learns from the gemara the power of connecting to Hashem and experiencing that "אין עוד מלבדו"—“There is nothing but Him.” He learns the effectiveness of this “segulah” from Rabbi Chanina in Sanhedrin 67 and explains that one who cleaves to Hashem in his thoughts and heart can remove the from himself the influence of any force or person. He must only set in his heart that "אין עוד מלבדו", there is no force in the world besides Hashem, since everything is one with Him.
Rav Dovid Soleveitchik, shlit”a, recounted two fascinating stories about the practical use of this concept in his family. “When the time came for my grandfather, the renowned Gaon, Rav Chaim of Brisk. to present himself in Warsaw for a preliminary check-up to determine if he was fit for the army, his father made the journey with him by train. Throughout the entire journey, they learned the famous segulah in Nefesh HaChaim and the Beis Halevi adjured him to be careful not to take his mind off the segulah for one instant, even during the examination.
“To the amazement of everyone—except the Beis Halevi and Rav Chaim himself—he was given a dispensation from serving in the army for no apparent reason.”
Rav Dovid explained, “Anyone inducted into the army during those years was in serious spiritual danger. He was required to violate Shabbos every week and eat non-kosher food at every meal. It is also well known, that my father and our family left the Nazi occupation with astounding miracles. Although he had a faked passport, it was still a clear manifestation of Divine providence that he got away. Interestingly, when they got to the Soviet border, a Gestapo guard suddenly began to chase them and screamed that they halt and give him money, but Stalin’s soldiers threatened him and he ran away.
“Later, my father explained that the entire time he had indeed focused on the segulah, but when he saw the border and thought he was out of danger he stopped. The minute he did so, the Nazi began to chase them!”