"'If it is a matter of strength, he is mighty! And if it is a matter of justice, who can challenge him?'" NIV translation
Job continues to speak of the despair of not being able to defend himself and his actions in the face of this perceived judgment. Once again, we see that he clearly understands the fact that God is all powerful but he does not see that the nature of God is goodness. We might be quick to judge Job as we have heard his story and know the outcome but we must also ask ourselves whether or not we sometimes fall into this trap of forgetting God's goodness.
"'Even if I were innocent, my mouth would condemn me; if I were blameless, it would pronounce me guilty.'" NIV translation
The word that is translated here as "blameless" is "tam", in Hebrew, and it usually speaks of someone that is morally upright especially someone who is gentle (humble) in spirit.
Now, Job speaks of the fact that, even if he was morally perfect, his own words would convict him in the eyes of God. Basically, what he is saying is that the very act of defending ourselves to God would be a sign of our arrogance (pride) and, in fact, a sin.
"'Although I am blameless, I have no concern for myself; I despise my own life.'" NIV translation
Job continues by explaining that, even though he is " a moral man", he does not have the ability to see himself as he truly is down deep in his soul. He goes on to say that he stays away from the sins of the flesh for the most part but realizes that it is not enough for him to be able to stand before God.
We remember that Job's friends have been accusing him of basically abandoning the faith of his ancestors and trying to hide his sin from them. Here, we see that he has not abandoned the faith of Abraham but he has a deeper understanding of that faith than his friends. His problem is the fact that he does not know of anyone who would have the status to speak to God on his behalf (he is searching for a mediator).