Analysis of Sonnet 14

Are these wild thoughts, thus fettered in my rhymes,
Indeed the product of my heart and brain?
How strange that on my ear the rhythmic strain
Falls like faint memories of far-off times!
When did I feel the sorrow, act the part,
Which I have striv'n to shadow forth in song?
In what dead century swept that mingled throng
Of mighty pains and pleasures through my heart?
Not in the yesterdays of that still life
Which I have passed so free and far from strife,
But somewhere in this weary world I know,
In some strange land, beneath some orient clime,
I saw or shared a martyrdom sublime,
And felt a deeper grief than any later woe.