This is a Wonderful Sermon! We cannot know why God brought suffering in Job's life but God in His mercy speaks to us and tells us. He sais that He is Sovereign.
All human works are bad (for unbelievers) or defiled by sin (for believers).
God saves whom He wants and hates whom He wants and "common grace" is just providence and does not prove anything.
The friends of Job misunderstood the providence of God, they sinned speaking lies about God.
This sermon is very good to explain God's Sovereignity and Holiness.