In Tibetan Buddhism, tantra is a very complete system of thought and practice specifically directed at people of different capacities. However, some practitioners in sutra, lacking an understanding of tantra, think they cannot practice tantra; some practitioners in tantra also cannot accept sutra. Therefore it is necessary to discuss the connection between sutra and tantra and sort out their differences and similarities. This will help everyone understand the contradictions, if any, in sutra and tantra, and prevent serious misconceptions from developing during the course of practicing the preliminaries.
~Depicted from GATEWAY TO VAJRAYANA PATH - Sutra and Tantra: Similarities and Differences