Reb Goldwag: Lech Lecha - Becoming Anointed

Why was Avraham chosen to be spoken to by Hashem directly, as opposed to the ten generations of great people before him? Why did Avraham challenge Hashem's destruction of Sodom by saying that there was an injustice in doing so? How does the world exist, despite the attribute of Hashem's justice? What is the concept of being anointed, and why specifically with oil? Why is it that Dovid is singled out as the author of Tehillim (psalms) if there are a total of 10 authors of the various chapters? Why was Dovid referred to as the 'ne'im zemiros Yisrael' - sweet singer of Israel? How can we become anointed?