«So am I as the rich, whose blessed key
Can bring him to his sweet up-locked treasure».
The poet grows more accepting of his separation from the young man, whom he likens to “up-lockèd treasure.”
So am I as the rich, whose blessed key
This image of the youth as a treasure unites the sonnet: In line 9, the poet writes, “So is the time that keeps you as my chest,” “chest” clearly referring to the locked treasure that is the youth. Also, the terms “imprisoned” in line 12 and “up-locked” are similarly linked.
Finally realizing that separation from the young man has its advantages, the poet deems it a blessing in disguise that he and the youth meet infrequently — encounters that he characterizes as “feasts so solemn and so rare.” The fewer meetings between the two, the more special and intensely emotional are those rendezvous.
English audio from YouTube Channel Socratica
Summary from Cliffsnotes.com