Oral transmission (Tib. lung) - It is important to receive an oral transmission (sometimes called 'aural transmission' or 'reading transmission') from a teacher, in order to create an auspicious connection with a particular text or practice. In the case of tantric texts, such as sadhanas or commentaries, this transmission occurs once one has received the relevant empowerment.
The reading transmission is passed down from master to student when the student listens to the teacher reading the text he holds the transmission for, transmission which goes back to the author of the text. In this way the student receives the blessing of the lineage without which he or she will not be able to understand the text fully in all its depth. Some teachers even consider improper to read a Dharma text one hasn’t received the transmission for.