All elements which are used on the Vajrayana path have a profound meaning. The body of the yidam is the unity of appearance and emptiness, the mantra is the unity of sound and emptiness, and the mind is the unity of awareness and emptiness. If one applies these elements to one's own practice, by abiding completely in this awareness, one can let the pride of the deity arise in oneself. But in order to do so one has to understand the real meaning of these things. It is not about simply visualizing oneself as the deity, because by the mere visualization one does not achieve this understanding.
Practitioners have to understand three things.
The view is that both kinds of reality make up an inseparable unity. For the path, the understanding that method and wisdom are a unity is important. Concerning the fruit, one needs the understanding that the two kayas which are achieved are a unity. Especially when practicing Mahamudra or Maha Ati, the understanding of these three elements is very important. Otherwise, one cannot realize the fruit through this practice.