Why do we read Parshat Bamidbar each year on the Shabbat prior to the holiday of Shavuot? Tosafot in Masechet Megillah (13b s.v. קללות) offers an answer. They say that we have this practice in order not to connect the curses of Parshat Bechukotai with the holiday of Shavuot which is when, according to the Mishnah in Masechet Rosh Hashanah, the world is judged about the fruit of the trees.
Rav Moshe Feinstein, in his Darash Moshe, points to a connection between Parshat Bamidbar and the holiday of Shavuot. He writes that there are people who feel that they will learn Torah but they will not reach a high מדרגה, spiritual level. Rav Moshe writes that the Torah chose to use the word שאו, raise, when counting the Jewish people (במדבר א:ב). This choice of word illustrates that each person can elevate himself by learning Torah when they see that they are worthy to be counted with the great personalities of our people. Therefore, prior to the holiday of Matan Torah, we are required to read Parshat Bamidbar which speaks about the counting of the Jewish people in the language of the נשיאות, leadership, in order to teach us if we accept this message properly, we will be able to accept the Torah and learn its message. We must realize that we all have potential to become great people.
In order to be successful in learning Torah we must realize the importance of Torah and we must have high self esteem so we can realize our true potential in Talmud Torah.
The Mishnah teaches us תלמוד תורה כנגד כולם, the study of Torah is equal in importance to all of the Mitzvot. If we understand the message of the connection between Parshat Bamidbar and the holiday of Shavuot, it will hopefully carry over and teach us how to properly fulfill all of the 316 Mitzvot.