Three quatrains, three moves
ABAB CDCD EFEF lets the rhyme start over twice. Each quatrain therefore feels like a fresh attempt at the same problem, and the reader is carried forward by the restart rather than by a single unbroken chain. That is the English sonnet's engine: repetition with variation, three times.
The practical effect on drafting is that you can write the quatrains out of order. If the third quatrain is the strongest, move it and rewrite the second to lead into it. In the Italian form this is much harder, because the octave is one unit and cannot be reordered without breaking its rhyme lock.
The couplet is an epigram, not a summary
GG is the only rhyme pair in the poem that sits side by side with nothing between it. That adjacency makes it sound like a verdict. If the couplet merely restates what the three quatrains already said, the poem ends twice and the second ending is dead weight.
The specimen's couplet does something narrower: it renames the wall. Nothing new happens; the same object gets a different category. That is the standard the form sets. Aim for a renaming, a reversal, or a sting — not a recap.
What changes when you switch from Italian to English
In English, rhyme sounds are scarce. There are roughly a dozen usable full rhymes for a word like stream, and most of them are tired. This is why the English sonnet uses four rhyme pairs and more end-stopped lines: the form adapted to the language's poverty.
The cost is that the English form has no fixed volta. The turn can arrive at line 9, line 13, or nowhere at all. To keep the poem from sagging, decide the turn's position before you write and mark it in the margin of your draft.