Midrasch zu Tehillim 19:12

More desireable than gold, or than greatly fine gold. (Psalms 19:11) We did not know who was more deisreable, Israel or the nations that worship stars and constellations. Solomon came and explained. In his shade I delighted and sat. (Song of Songs 2:3) In guarding them is much reward [eqev rav] (Psalms 19:12) — anyone who guards the Torah is made a rabbi [rav]. Another interpretation: anyone who guards the Torah to its end [eqev] is a rabbi [rav], and we open doors for him.