When Reb Naftali Amsterdam zt'l came to live in Yerushalayim (from chutz l'aretz), he came to Reb Shmuel Salant zt'l. He said, "Everyone is obligated to have a Rav, as it states (Avos 1:6) רב לך עשה. Please, tell me who should be my Rav here in Yerushalayim?" (Reb Naftali Amsterdam was already very old; he was a great tzaddik, and in the past, he had served as the rav in several cities. Nevertheless, he still felt that he needed a rav.)
Reb Shmuel Salant told him, "The gaon, Reb Yosef Chaim Sonnenfeld, gives a shiur in Mishnayos every day between Minchah and Maariv. Go there and listen to his shiur. When you hear something new from him, he will be your Rav."
The next day, all the people who attended Reb Yosef Chaim's daily shiur were shocked to see the old tzaddik, Reb Naftali Amsterdam, come to listen to the shiur. The shiur was a simple shiur, intended for baalabatim, simple people. They learned Mishnayos. Why would Reb Naftali join the shiur?
Actually, Reb Naftali enjoyed the shiurim. Although they were simple shiurim that anyone could understand, Reb Naftali understood the depths of Reb Yosef Chaim’s shiurim. With clarity and simplicity, Reb Yosef Chaim explained the Mishnayos in a manner that answered many difficult questions. Nevertheless, Reb Naftali didn't hear anything that he didn't already know, and he was waiting for the moment when Reb Yosef Chaim would become his Rav.
One of the chapters of Mishnayos Sanhedrin is called חלק (because it begins with the renowned phrase, ַבָּאה לָעוֹלָם חֵלֶק לָהֶם ׁיֵש יִשְׂרָאֵל כָּל), and Reb Yosef Chaim Sonnenfeld was teaching the Rambam's introduction to this perek. In this introduction, the Rambam teaches the 13 אני מאמין. Reb Yosef Chaim elaborated on the th Ani Maamin, the belief in the coming of Moshiach. He repeated the Gemara (Sanhedrin 97a) that Moshiach will come הדעת בהיסח, when people aren't thinking about it, and aren't expecting it.
At this point, Reb Naftali spoke up for the first time. He asked, "How can one forget that Moshiach is coming? One of the questions that will be asked of each person when they come to heaven is לישועה צפית, 'Did you wait for the salvation?' (Shabbos 31a). Also, in every tefillah, we affirm כל קוינו לישועתך כי היום, 'We await the coming of Moshiach all day long'. In Kedushah, we say in a loud voice, לך אנחנו מחכים כי עלינו ותמלוך, 'Be our king, because we are waiting for You.' So, is there a Yid who has הדעת היסח from Moshiach?!"
Reb Yosef Chaim replied, "Imagine that right now, the door opens and someone comes in and says, 'Rabbosai! Why are you all sitting here? Moshiach has arrived!" Everyone will be in shock, and they will ask, "Is it true? Could it be?' Now I ask you, is there a greater הדעת היסח than that? When people wait for a guest, and then they hear that the guest has arrived, no one would wonder or question whether it is true. They will get up and greet him. So, why should it be surprising for us to hear that Moshiach came? This is הדעת היסח."
Reb Naftali's face lit up with joy, and he stood up and said, "It is true! It is true! I have a rav. I learned something new."
