v. 8: The commandment of the LORD is pure, enlightening the eyes. This is set against what Eve in Eden saw of the fruit of the knowledge tree. Genesis 3:6 - that it was pleasant to the eyes. Eve made the commandment of the LORD impure.
v.9: The fear of the Lord is not something you are involved with only when you are a sinner. It is everlasting from prefall to the new heaven and Earth, because it is as clean as the creator-creation distinction.
v.43-45: Unlike Solomon who mingled with the strangers, David neither mingled nor submit to them, but ruled over them, made by God, before God. A true type of Christ.