When the first edition of SHAKE-SPEARES SONNETS hit the presses in 1609, each sonnet was assigned a number (1-154) instead of its own. (Hey. Have you ever tried coming up with a bunch of titles after cranking out 154 poems? It's tough work, Shmoopers.)
We're not quite sure who came up with the order of the sonnets because Shakespeare probably didn't have anything to do with their publication. But we do know the order is pretty important. Why? Because when we read them, the sequence unfolds like a complicated story that involves some recurring "characters" and situations. In other words, it's a rather loosey-goosey story, all in 152 poems.
Sonnets 1-126 all seem to be addressed to a young guy critics like to call the "Fair Youth." Sonnets 127-152 seem to be mostly about the speaker's sordid affair with a woman who's got dark physical features and shady morals. (That's why literary critics like to call these the "Dark Lady" sonnets.) In Sonnet 147, the speaker accuses his unnamed lover of being "as black as hell, as dark as night" (13-14), which is why we think he's talking to the same "dark" mistress that shows up in so many of the other poems.
One last thing, Shmoopers. Sometimes sonnets are referred to by their first lines, which is why #147 is often called "My love is as a fever, longing still."