Answer:
I begin your sentences.
I get dirty when wiping things clean. What am I?
You use a knife to slice my head but you weep beside me when I am dead
I have a brother. However much we run we do not reach each other.
Oh lord! I am not worthy! I bend my limbs to the ground. I cry yet without a sound. Let me drink of waters deep. And in silence I will weep.
Whoever made me don't want me. Whoever bought me don't need me. Whoever use me don't know me.