With this line, the author introduces and establishes a point that attempts to disprove the idea that love is all. This is a common phrase, but the poet uses specific examples of actual things that are not obviously not love. The point is that love cannot actually be all, so describing physical items is how the author starts.
This furthers the point of disproving that "love is all" by using obvious factors of life that have nothing to do with love.
"Love can not fill the thickened lung with breath,"
A poetic device used in the sonnet is personification. It is given to the concept of death in the line "Yet many a man is making friends with death". Death is personified as a person that people can be friends with. This is to describe and symbolize the Turn in the sonnet in a way that is easy to interpret.
The Turn in the sonnet appears with the line "Yet many a man is making friends with death. Even as I speak, for lack of love alone". Before the turn, the poet is simply explaining what love is not, despite the belief that love is all. After the turn, however, the focus shifts to the state of love. The poet discusses how they would treat someone else's love under certain circumstances. They then clarify that they would likely never give up their love, showing how this is a love poem for someone else.
"I might be driven to sell your love for peace,"
The speaker claims that they may need to give up their love in some scenarios, though they would have to be very poor circumstances.
"It well may be. I do not think I would."
THEMELove may not be all, but it is strong enough to keep people together through hard times.
The poet still says that they would likely never give up their love, no matter the situation.