Under God?: Who is God?

What does lord of host mean?

It means Lord of angels/angelic army. 

Do you have to name every sin and ask for forgiveness for every sin? What if u forget one? 

If you had to name every sin, I think we'd all be in trouble because there are so many sins we committed prior to turning to Christ and to have to name every single sin would be impossible. But that doesn't excuse not naming specific sins that you know you need to repent of. So ask forgiveness for specific sins and then ask God to forgive you even for the sins that you don't remember. 

IF...God is holy; all that he established is holy. Why if? Is there some question about his holiness? I'm baffled by its usage.

First, I don't know that "if" always implies a question. It can be a word used to imply a statement, as well. As an example,"If chicken is raw you shouldn't eat it" is a statement.

However, I used "if" at the beginning of the sermon for a different reason. At the beginning, I was addressing all of the other starting points a person could have for why they believe what they do if they don't start with God. And I asked them to not tune me out as I talk about God because God is the morally excellent (holy) person that they wish existed. So I said "if" for the unbelievers in the room. By the end of the sermon, once I had proven that God is holy and asked them to compare their starting point with God, I stopped using the word "if." You may have missed it, but I transitioned the language to, "Because God is holy, all that He establishes is holy." 

Hi Josh! Have you listened to or read RC Sproul “The Holiness of God”? Good stuff!

Yes. I have read Sproul’s book. It’s a good one!