The function of a Dharma protector is to arrange all the outer and inner conditions of our lives so that everything that happens to us is perfect for our swiftest possible enlightenment. But Dorje Shugden is more than just a Dharma protector, he is also a wisdom Buddha. It is not enough to just know that the outer and inner conditions of our life are perfect for our enlightenment, but to be able to take full advantage of these conditions we need to understand and realize directly how (or in what way) they are indeed perfect. When we have the wisdom which realizes how our conditions are perfect, then we can fully take advantage of them and move most swiftly to enlightenment. The blessings of Dorje Shugden bestow upon us this wisdom of realizing how the conditions he has emanated for us are in fact perfect. Then we are not only happy with everything, but can use everything most effectively to advance along the path.
When we realize the emptiness of ourselves, all beings and Dorje Shugden then we realize that his power is not limited to just arranging perfect conditions for ourselves and bestowing upon ourselves the wisdom realizing how our conditions are perfect, but we can also invoke him to accomplish this same function for each and every living being. We pray to him that he arrange all the outer and inner conditions for each and every being so that whatever happens to them is perfect for their enlightenment. He can then bestow upon us the wisdom that sees directly how whatever arises in the life of any living being is in fact perfect for their enlightenment. Then, we can share our point of view with others, helping them to see their lives and challenges as gifts from all the Buddhas designed to quickly deliver them to the bliss of full enlightenment.
From our perspective, Dorje Shugden is the same being as the wisdom Buddha Manjushri. Manjushri appears in two aspects, as Je Tsongkhapa to lead us along the path and as Dorje Shugden to arrange all the conditions of our practice. It is therefore impossible to reject one without rejecting the other two. Since we all agree that Manjushri and Je Tsongkhapa are perfectly reliable Buddhas, since Dorje Shugden is for us just a different aspect of this same being, Dorje Shugden is also perfectly reliable. We cannot reject him without rejecting the others. Since we cannot reject the others, we cannot reject him.
Kadampa Working Dad 
Right now to me Dorje Shugden is an idea. A concept. A way of protecting our own karma. A way of looking at the things that happen to us with a pure mind of faith. Some people love it some people do not. But in the end, pure faith is more powerful than all protectors, since this is what they really want from us. Faith and compassion and real pure minds. We begin to see Dorje Shugden at work everywhere.
Whether we believe or not will not stop enlightened beings emanating in various forms to help us out.