So in line 1 the guy has strong feelings for the girl but the girl isn't interested in him by saying my love is like fire to ice and the fire is representing the guys love to the girls love which is represented by ice.
My love is like to ice. And i to fire
So in line 2 it talks about how the girl is not feeling the same for the guy and that the guy try's to mix his fire with her ice
How comes it then that this her cold so great is not dissolved through my so hot desire,
In this poem Edmund compares the case with the aspects of ice and fire that he has refused. Imagination is a poetic device used when you read something to paint a scene in your mind. In this scenario, the flames of a fire will attack you, eaten up by ice crystals.
The Turn in the poem/sonnet is about a guy and a girl and that a guy has feelings for this girl but the girl doesn't feel the same way towards the guy and that love is powerful and that it can be bad and love can even hurt the mind
Such is the power of love in gentle mind, love has the ability to change someone's life and the ability to have a smooth mind
That it can alter all the course of kind. meaning that love is so strong that it can hurt the people that's close to you. And the theme in this poem/sonnet is about love and how powerful it is to be in love and that love can break and make society and mankind.