Short Answer 
The answer discusses Shakespeare’s exploration of the temporary nature of beauty and the enduring essence of love and youth. It highlights that while physical attractiveness diminishes over time, the emotional experiences associated with youth and love hold greater significance, encouraging appreciation for deeper connections beyond mere appearances.
Step 1: Understanding the Meaning
The lines “And every fair from fair sometime declines, By chance, or nature’s changing course untrimm’d” highlight the idea that beauty is temporary. This suggests that no matter how attractive someone may seem, time and other factors will inevitably lead to a decline in physical beauty. Shakespeare conveys this message to reflect on the fleeting nature of aesthetic appeal in life.
Step 2: The Impact of Love and Youth
In these lines, Shakespeare also delves into the themes of love and youth. He mentions the spirit of youth, which remains vibrant and enduring, contrasting it with the fading beauty that everyone experiences over time. This shows that while physical appearance may diminish, the essence of youthful emotions and love can persist.
Step 3: The Comparison Between Beauty and Spirit
Shakespeare draws a critical comparison between youthful spirit and beauty. He emphasizes that although physical beauty can fade, the emotional highs related to love and youth are more significant and lasting. This reflection encourages readers to appreciate deeper connections rather than just superficial appearances.