Each of these critics agree in the essence of the Sonnet and its portrayal of what love really is and what it can withstand, for example, the test of time and the fading of physical attraction of the object of our love.
The passage emphasizes that all the critics agree on the fundamental message of the Sonnet, which is about the nature of love and its ability to endure even when faced with challenges like the passage of time and the fading of physical attraction.