This is actually the twenty-first century.
The line (either 9 or 10) which you are emphasising indicates a change of tone does not function in this way. In fact, if I was being pernickety, I could say that I fail to see how it connects either with the lines before or the lines after.
A sonnet, as I carefully pointed out in my first posting, is a particular poetic form which depends upon structure for its effect.
There is a well known syllogism which demonstrates false logic as follows:
All tigers eat meat;
That animal is eating meat;
Therefore that animal is a tiger.
or if you prefer :
All sonnets have fourteen lines;
This poem has fourteen lines;
Therefore this poem is a sonnet.
And before anyone rushes for their revolvers, yes I do know that there are sonnets which have 16 lines and 12 lines (Hopkins's experiment which he called a curtal sonnet), though strictly speaking they are not sonnets at all and are (more to the point) not very good poems structurally.
In fact it might be instructive to read Hopkins's curtal sonnets to learn what happens when you break the rules. Bear in mind Hopkins's own perceptive remark about "downright prolapsus or hernia" that results from tying sestet to octave by rhyme.
Also try to understand Louis Macneice's remark: when he said: "In any poet's poem the shape is half the meaning".
Just one final peeve: what is the purpose of the apostrophe after the letter "s" in years?