If Thou Must Love Me, Let It Be For Nought

The title creates curiosity about conditions posed to love somebody. It is not a coincident that the title is repeated in the first line, thus reinforcing the same curiosity. Indeed, all the sonnet is a lyrical investigation about the condition of love on the part of the speaking voice.

Not only the first line repeats the content of the title but it puts the message its self in the better focus. Inviting the lover to love just for love. 

Since the second line the exclusive thought about love (signalled by the word "only", at the centre of the line) is remarked and the expression, the phrase "for love's sake" becomes the condition justifying the all sonnet.

All the remaining sonnet part provides the argumentations for that choice.

The message which is immediately clear even to the common reader is reinforced by the direct invitation of the speaker to her Beloved not to use mechanical words (like the ones covering lines from 3 to 6 expressed in direct speech).
The speaking voice seems to tell her interlocutor that, in her opinion, love is not such when you love somebody for (her smile - her look - her way speaking gently).

Love implies something different going beyond attitude. Love does not bring him simply "a sense of pleasure".

If Thou Must Love Me, Let It Be For Nought

The title creates curiosity about conditions posed to love somebody. It is not a coincidence that the title is repeated in the first line, thus reinforcing the same curiosity. Indeed, all the sonnet is a lyrical investigation about the condition of love on the part of the speaking voice.

The first line does not only repeat the content of the title but it puts the message itself in a better focus, inviting the lover to love just for love. 

Since the second line the exclusive thought about love, signalled by the word only, at the centre of the line, is remarked and the expression for love's sake becomes the condition justifying the all sonnet.

All the remaining sonnet part provides the argumentations for that choice.

The message that is immediately clear even to the common reader is reinforced by the direct invitation of the speaker to her Beloved not to use mechanical words, like the ones covering lines from three to six expressed in direct speech.
The speaking voice seems to tell her interlocutor that love is not such when you love somebody for her smile, her look, her way speaking gently.

Love implies something different going beyond attitude. Love does not bring him simply a sense of pleasure.

In my opinion this analysis should be improved in:

The analysis of the title

The analysis of the layout

The structural analysis

The connotative analysis, in particular the phonological level