They have been speaking of Buddha-nature as though it were something that could be described, as though it were similar to the "soul" of other teachings, but it is not.
The concept of an "ego-personality" is something that has been imagined by a discriminating mind which first grasped it and ten become attached to it, but which must abandon it. On the contrary, Buddha-nature is something indescribable that must first be discovered. In one sense, it resembles an "ego-personality" but it is not the "ego" in the sense of "I am" or "mine."
To believe in the existence of an ego is an erroneous belief that supposes the existence of non-existence; to deny Buddha-nature is wrong, for it supposes that existence is non-existence.
This can be explained in a parable. A mother took her sick child to a doctor. The doctor gave the child medicine and instructed the mother not to nurse the child until the medicine was digested.
The mother anointed her breast with something bitter so that the child would keep away from her of his own volition. After the medicine had time enough to be digested, the mother cleansed her breast and let the child suck her. The mother took this method of saving her child out of kindness because she loved the child.
Like the mother in the parable, Buddha, in order to remove misunderstanding and to break up attachments to an ego-personality, denies the existence of an ego; and when the misunderstanding and attachments are done away with, then He explains the reality of the true mind that is the Buddha-nature.
Attachment to an ego-personality leads people into delusions, but faith leads people into delusions, but faith in their Buddha-nature leads them to Enlightenment.
It is like the woman in a story to whom a chest was bequeathed. Not knowing that the chest contained gold, she continued to live in poverty until another person opened it and showed her the gold. Buddha opens the minds of people and shows them the purity of their Buddha-nature.