The relative ages of the speaker and the young man are emphasized in three sonnets: 71, 73, and 74. The speaker is a much older man and contemplates his own death. In doing so, he wonders what effect his death will have on the young man.
In "Sonnet 71" the speaker pleas with the young man not to mourn, not to be sad, once the speaker is dead. The speaker wants the young man to get on with his life. He does not want the young man to remain in sadness for a long period of time. He even tells the young man not to read his poems (in the third quatrain) if, by doing so, that causes even greater grief for the young man. The last line of the quatrain reinforces the message:
(line 12)
In other words, the speaker is telling the young man to forget the speaker and his love for the speaker. The speaker does not want the young man to be miserable.
The shift in this poem occurs in the final couplet. There is a second reason the young man should not moan or be miserable -- at least not in front of other people. Other people might mock him or make fun of him -- and the speaker -- when they hear about the love that existed between the two of