Guru is the main deity in the center of all the mandalas
We need to understand the Guru is inseparable from all the Buddhas, the Bodhisattvas and all the mandala. The Guru is the main deity in the center of all the mandalas. That is taught to high masters like Longchenpa, Jigme Lingpa and all of them did practice in the same way. When Like Jigme practiced Guru Yoga, he visualized Longchenpa as the Buddha. There was no impure thought towards Guru. For the Dharma practitioners, specifically Vajrayana practitioners, the Guru is very important. Therefore, one takes time to learn about the Guru, the qualities of the Guru. And the conditions to be a Guru is very important so we should not accept a [person to be] Guru that is not qualified. Because we have to rely on the Guru for the rest of our life – not only in this life but many lives in the future.
People sometimes don’t understand these important things and very hurry in accepting someone to be “guru”. Then, since the “guru” maybe unqualified, then problems will arise later. That will definitely happen because the Guru is not qualified. So, it’s important for people to be patient, be smart, to be honest and to take some time to investigate – to study, to be familiarized with the Guru, and then accept, and be a good student.
Hungkar Dorje Rinpoche, “GURU YOGA: Bless Me So That Delusion on The Path Will Cease”