What does the cryptic crossword clue "What one wants above all is the reader's involvement (6,6)" mean?

The wordplay uses an anagram. anagram of IS + THE + READER'S = HEARTSDESIRE The answer is HEARTSDESIRE.

What one wants above all is the reader's involvement (6,6)

Guardian Cryptic #23778 | 12 Across | 2006-05-29 flower