«When to the sessions of sweet silent thought
I summon up remembrance of things past».
The poet repeats Sonnet 29’s theme, that memories of the youth are priceless compensations — not only for many disappointments and unrealized hopes but for the loss of earlier friends: “But if the while I think on thee, dear friend, / All losses are restored and sorrows end.” Stylistically, Sonnet 30 identically mirrors the preceding sonnet’s poetic form.
When to the sessions of sweet silent thought
This sonnet is one of the most exquisitely crafted in the entire sequence dealing with the poet’s depression over the youth’s separation (Sonnets 26–32). It includes an extraordinary complexity of sound patterns, including the effective use of alliteration — repetitive consonant sounds in a series of words — for example, both the “s” and “t” sounds in “sessions of sweet silent thought.”
But alliteration is only one method poets use to enhance the melody of their work. Rhyme, of course, is another device for doing this. A third is assonance — similar vowel sounds in accented syllables — for example, the short “e” sound in the phrases “When sessions” and “remembrance”. In this case, the short “e” sound helps unify the sonnet, for the assonant sound both begins — “When” — and concludes — “end” — the sonnet.
Contributing to the distinctive rhythm of Sonnet 30‘s lines is the variation of accents in the normally iambic pentameter lines. For example, line 7 has no obvious alternation of short and long syllables. Equal stress is placed on “weep afresh love’s long,” with only slightly less stress on “since,” which follows this phrase. Likewise, in line 6, “friends hid” and “death’s dateless night” are equally stressed. This sonnet typifies why the Shakespeare of the sonnets is held to be without rival in achieving rhythm, melody, and sound within the limited sonnet structure.
English audio from YouTube Channel Socratica
Summary from Cliffsnotes.com