God speaks to Moshe on a regular basis.  The formula that usually introduces this communication is וידבר ה' אל משה לאמר, God spoke to Moshe, saying.  However this parashah and the book of VaYikra opens with God’s summoning Moshe before He speaks to him: ויקרא אל משה, God called to Moshe.  Instead of just speaking to Moshe, God invites him to listen first.  God’s invitation to Moshe can teach us about what it means to listen to God’s voice and to accept His personal invitation to learn His Torah.