In the passage below, what is the point of the story of the Turk in Aleppo?

When you shall these unlucky deeds relate,

Speak of me as I am. Nothing extenuate,

Nor set down aught in malice. Then must you speak

Of one that loved not wisely, but too well.

Of one not easily jealous, but being wrought,

Perplexed in the extreme. Of one whose hand,

Like the base Indian, threw a pearl away

Richer than all his tribe. Of one whose subdued eyes,

Albeit unused to the melting mood,

Drop tears as fast as the Arabian trees

Their medicinal gum. Set you down this,