Mentally challenged people are not so heavily invested in their minds and therefore they can be freer and more in touch with their inner selves.
I have personally known people with Downs syndrome and other learning disabilities who have shown wisdom, tolerance, and a love of life that far more educated people were never able to attain.
Several years ago I had a personal trainer who had Downs syndrome. He understood the human body with intuitive acuity and communicated it well in his own way. I learned a great deal from him and his sage-like approach to strength and skill. He was patient and kind and I will never forget him. The strength of his soul far outshone the limitations of his physical brain.
It is a big mistake to think that intellectual giftedness and the Soul are interrelated. Again, the intellect has very little to to with the soul and can often block its manifestation in our lives. The mind is a very good analytical tool but the soul come from a different area, more like from a combination of the heart and the gut. Therefore, if a person is mentally challenged, he or she may be more receptive to the qualities of Soul and be more tuned into the pulse of the Universe than those of us who think we are our minds.