Analysis of Holy Sonnet IV: Oh my black soul!

Oh my black soul! now art thou summoned
By sickness, death's herald, and champion;
Thou art like a pilgrim, which abroad hath done
Treason, and durst not turn to whence he is fled;
Or like a thief, which till death's doom be read,
Wisheth himself delivered from prison,
But damned and haled to execution,
Wisheth that still he might be imprisoned.
Yet grace, if thou repent, thou canst not lack;
But who shall give thee that grace to begin?
Oh make thy self with holy mourning black,
And red with blushing, as thou art with sin;
Or wash thee in Christ's blood, which hath this might
That being red, it dyes red souls to white.