Bamidbar is read on the Shabbat before Shavuot, and the rabbis have connected the two. One interpretation is that since the Torah was given in the open, in a place that is not owned by anyone, then anyone may come and accept it. Another interpretation is that the wilderness is free, so is the Torah free. However, the most spiritual reason is that the desert is a place of silence, with no distractions. In Kings, Elijah heard the still small voice because he was listening. However, Judaism is highly verbal, and silence is frequently seen in a negative light. But not all silence is bad.
