Shlah haKodesh - there is no contradiction between the specific voice that spoke at Har Sinai and the never ending voice of Hashem that is still "speaking" today. Only by learning Torah lishmah (for its own sake) can we hear the "voice" of Hashem. The Torah is in galus (exile). When we learn Torah we "redeem" Hashem. We must beg Hashem to uncover the husks that cover the Torah. We were sent into this world to reveal the Torah. Learning connects us to prophecy.