Excerpt:
In his talk, Rav Soloveitchik attested that his family tradition confirms the attempt of the Alter Rebbe to visit the Vilna Gaon in an attempt to persuade him to abandon his opposition to Chassidus (except that in the Brisker family tradition it was Rav Levi Yitzchok of Berdichev who accompanied the Alter Rebbe on this visit, whereas according to Chabad tradition, as recorded by the Alter Rebbe himself in his Igros Kodesh letter 52, it was Rav Mendel Horodoker).
The Rav then revealed that the reason the Vilna Gaon refused to meet the Alter Rebbe was because the Vilna Gaon was so awestruck by the holy countenance of the Alter Rebbe (which he saw through a crack in his door) that he felt that if he allowed the Alter Rebbe in, he would be persuaded to leave hand-in-hand with the Alter Rebbe and would (not only desist from opposing him, but, on the contrary, would) join him in spreading Chassidus
The Rav contended that although Rav Chaim Volozhiner wrote his magnum opus “Nefesh Hachaim” at the request of the Vilna Gaon with the express purpose to contradict and refute the contents of the Tanya and demonstrate that its philosophy is contrary to the accepted beliefs of Torah – in reality, the opposite is true and the Nefesh Hachaim overwhelmingly confirms the tenets, principals and beliefs articulated by the Alter Rebbe in the Tanya (and the areas of apparent disagreement are marginal and primarily semantical).