Ooh... good question...
Sorry it took me so long to get on here and read it Brian.
This is actually something I’ve thought a lot about over the last several years.
First of all, you’re right in saying that there’s a difference in the Old Law and the New Law. For instance, do you know anyone who still offers sacrifices or travels to Jerusalem regularly for worship? Those are things in the Old Law that we don’t have to keep anymore. Furthermore, the Old Law was solely written for the Jews, who were God’s chosen people before Christ came to offer salvation to everyone.
Galatians and Hebrews talks in depth about the transition between the Old and New laws, as well as several other New Testament passages. But instead of trying to go into a lot of detail about all of that right now, I’m going to refer you to a couple of articles I’ve written about it in the past. And if you have questions about those, then we can delve a little deeper:
Old Law vs New Law thread from message board
It’s Not Fair - God of OT vs God of NT from my blog
Grace vs Law from my blog
The Mystery Revealed from my blog
Those are probably the most relevant posts I’ve done about that subject. They probably aren’t the best out there, but it’s a start anyway...
As far as instrumental music in worship is concerned, you won’t find churches of Christ participating in that because we aren’t commanded to do so in the New Testament. In Ephesians 5:19 and Colossians 3:16 we’re told to sing psalms, hymns, and spiritual songs. Since we’re only told to sing, that’s what you’ll find in churches of Christ.
Now, I’ll also say this: there seems to be some ambivalence about the word "psalm" that’s used there. Some definitions for that word include the idea of singing with musical accompaniment, and other definitions don’t. Based on that, some people don’t believe they can actually
condemn someone for using instruments in worship, while others still believe that the practice would be forbidden. That’s where some personal judgment has to come into play.
But we can definitely say with confidence that simply singing is obviously acceptable to God. Trying to go beyond that might be a little riskier...
I hope this has helped some. Please let me know if you have any other questions or if I’ve been unclear about any of it. I know I haven’t really addressed everything you asked, but we can talk more about it Wednesday night, if you want (it’s getting past my bedtime!).
later!