In Blake's London there were, of course, many others who claimed to be visited by angels and to talk to the dead, but Blake made art out of it. Among many beautiful thoughts Blake expressed, that was one of the most beautiful. His art strives for ecstatic revelation on the level of visions and rises to the heights of his great verse, sometimes. Apprenticed to an engraver of traditional style named James Basire, Blake remained dedicated to contour and line even in later years, when a linear style made him seem outmoded. He hated colorists like Titian and Rubens, and he especially despised Correggio, probably because Reynolds, Blake's bugbear, admired him.
Color carries much of the expressive baggage.
He was an exquisite colorist. Even the biggest prints and watercolors are not so big, although their colors give them presence out of proportion to their size. Size doesn't indicate significance by itself, but it is probably not meaningless that the best work by Blake remained on the scale of a book, albeit a big book sometimes. Like many artists, Blake had formulas and fell back on them. He knew not just Michelangelo, but also physiology, as the literary scholar Marilyn Butler points out in one of the more interesting essays in the show's catalog, and his figures are absurdly muscle-bound hunks with every sinew described.