Dear Forum Readers
One of the arguments made by DS proponents are DS's previous incarnations have been an enlightened beings. So it is impossible for DS to be born as a Gyalpo Spirit through the force of Karma. To say that, is implying that enlightened beings can degenerate to such as low state, which is impossible.
From what I learned, the characteristics of enlightened beings is they are omnicients and not controled by by the force of karma.
If he was an enlightened being, Tulku Dragpa Gyeltsen should be omnicient, can see through the past and future lives of himself and other beings. So why he needed to be reminded by a spirit like Nechung that he had promised to rise as a unique Dharma Protector through eating the rice blessed by Nechung, the spirit?
I believe there are many factors that contribute to this. Personally, I think that it is because of Tulku Dragpa Gyeltsen's humility that made Nachung remind him.
I remember reading a story about a mahasiddha, whom was enlightened from birth as he came to the world from a lotus. Although he is enlightened, he searched for a Guru (of which he found) and served his Guru perfectly. After much observation, his Guru then said why is the mahasiddha here as he is already an enlightened being... Upon his Guru's approval that he is enlightened, the mahasiddha then ascended to Tushita in that very body. I believe it is the same in Tulku Dragpa Gyeltsen's case.
It could also due to the time and age that Tulku Dragpa Gyeltsen was in... 350 years ago is not too long ago, and at that time, many great tulkus and lamas that reincarnate do not concentrate on having 'mystical' powers anymore... because the minds of the people at these time can no longer accept it. Instead of thinking the lama with great power as a great being or Bodhisatvva, they may get sceptical or even worst, try to exploit the lama. So perhaps because of this, Nechung had to 'remind' TDG.
Another way of looking at this is perhaps because of the collective karma of the people at that time prevented TDG to manifest as a Dharma Protector.
Dorje Shugden is an enlightened being, and to say otherwise is total ignorance and reflects one's selectiveness on the Dharma. The very fact that DS manifesting 4 eminations shows his enlightened ability to aid being of the realms. To reject or talk ill of DS is similar to disparaging all the Buddhas, as it is not DS that they're rejecting but the qualities that DS exhibit, which is an enlightened mind.