Sonnet 7 compares human life to the passage of the sun ("gracious light") from sunrise to sunset. The sun's rising in the morning symbolizes the young man's youthful years: Just as we watch the "sacred majesty" of the ever-higher sun, so too does the poet view the youth. The sun's highest point in the sky resembles "strong youth in his middle age." However, after the sun reaches it apex, its only direction is down. This downward movement represents "feeble age" in the youth, and what is worse than mere physical appearance is that the people who looked in awe at the youth's beauty will "look another way" when he has become old. In death, he will not be remembered.
As usual, the poet argues that the only way for the youth to ensure that he is remembered after he dies is to have a child, making it clear that this child should be a son. Two possible reasons why the poet wants the young man to have a son and not a daughter are that, first, a son would carry on the youth's last name, whereas traditionally a daughter would assume the last name of her husband, and second, the word "son" is a play on the word "sun" — it is not coincidental that in this sonnet, which incorporates the image of the sun, the poet makes clear for the first time that the young man's child should be a son.