In common parlance, especially among 'liberals', the self is 'bad': associated with selfish, self-centered, self-righteous, and a host of other derogations. In modern psychology it has other connotations; the concept evoked by the above words is ego. With Jung especially Self is the goal of individuation or the Christ-image.
In the Bible the word is pretty good: "Thou shalt love thy neighbor as thyself."
A good long generation ago an atheistic psychotherapist named Erich Fromm wrote a unique little book called The Art of Loving; he discussed the trinity of love found in the Great and Second Commandments (God, Others, Self), and he emphasized something that has been commonly overlooked when considering them: Self!
You cannot love God or neighbor without loving yourself; these three attributes, like the Holy Trinity, are all facets of the same reality. If you doubt that, read the book. You may get a copy for 38 cents.
Blake's attitude toward the self was uniquivocal. The 'bad self' he called Selfhood; to reach Eternity it must be annihilated. (He had not read Erich Fromm!). The furnace functions primarily to annihilate the Selfhood: "Thy dross to consume, and thy gold to refine" as in You tube. For a prettier one look at
Plate 15 of Milton. That's a great big Selfhood and a much smaller, but more muscular Self.