This discourse was taught by the Rebbe on Shabbat Bemidbar, following Lag B'Omer (which was on the previous Sunday).  This Shabbat was just before the outbreak of the Six Day War in Israel. 

It focuses on a story in the Zohar which describes how Rabbi Shimon bar Yochai was able to make the rain fall after a drought, by saying a Torah teaching.  Other Sages would pray for rain, or even fast.  The discourse explains the special power shown by Rabbi Shimon bar Yochai in that he was able to bring rain by saying a Torah teaching, and how this applies to every Jew.