Mary sat at his feet while listening attentively to all Jesus was teaching. She adopted a student's attitude towards her beloved Raboni.
Martha instead was preoccupied with dinner preparations and needed help. Much as we worry about our many responsibilities and wish for others to help us. So Jesus tells her this and then adds that Mary has chosen the best part.
So I say that enjoying Jesus' presence and listening closely to his words is what is most important. We must not miss this divine appointment. Only then we will be able to do everything in God's strength and love.
