Visualization meditation is a major Vajrayana practice. Why is it important? During one of the teaching sessions with the Vajra Master Jinke Xuanlei, he explained that wisdom is gained through introspection and self-reflection, yet ultimate wisdom in Vajrayana is gained through visualization.
Visualization in Buddhist practice is a method in meditation. Cultivators visualize an object in their mind, which means they imagine seeing it in front of them, or they set an intention in their mind. This practice relies on the ability of the mind to create things as solid and real as possible. Gradually, with consistent training, cultivators are able to manifest a whole other realm, just like how cosmic buddhas with a Dharma light body are able to manifest their own realms and not being limited to the one and only physical world that beings with the five senses perceive.