What is the meaning of Shakespeare's Sonnet 30?

In Shakespeare’s Sonnet 30, the persona spends the time reminiscing on his past. At these moments he remembers his friends he has lost in death, and he again feels the pain that had once been erased(line 14) His grief is renewed and he uses expressions like ‘wail’(line 4), ‘drown an eye’(line 5), ‘weep’ (line 7), and ‘moan’ (line 8) to relay his pained feelings and tears shed during those memories. When he goes on to talk about ‘old woes’ (line 4), ‘long since cancelled woe’ (line 7), ‘a vanished sight’ (line 8), ‘grievances foregone’ (line 9), and ‘fore-bemoaned moan’ (line 11), he is reiterating his ability to call to mind accounts of his grief that had long been over but now is refreshed by his new thoughts. The persona doesn’t mind the tears though, since he is the one summoning these remembrances (line 2) as he makes the effort to live once more in the past (lines 9 to 12) and commit to mind his dear friends.

William Shakespeare’s Sonnet 30 focuses on the relationship between past and present and between pain and pleasure. The speaker spends most of the poem considering the role of memory and nostalgia, both of which renew and prolong the pain that they had previously experienced. Once a person has suffered a serious loss, the speaker claims, memory will not allow them to let go. Reliving the events causes just as much pain as the original event did.
The harsh realities of life seem to concern the speaker—perhaps even overwhelm them. Balancing out this morbid fascination, however, is the idea that human affection and companionship can, and perhaps should, override negative memories. The speaker ends the poem with positive reflections on friendship and loyalty.