Part of the reason for "the fall" of mankind is that we like to do things ourselves. We like to think we don't need God. That's the reason Satan told Eve that if she ate of the fruit she would be like God. She already was like God. He created her in His own image. Yet Satan wanted Eve to feel like God was cheating her in some way. And she did, and she ate.
But we all do it. We take matters into our own hands. We do it our way, as the song goes.
I think the Old Testament is like a progression of ways that won't work. Not because they can't work, but because people won't live by them. It's like God is saying "See, you've tried this, and here's what happened...."
At one time God spoke to all the fathers, and that didn't work. Then He spoke to prophets in all the nations and that didn't work. Having people stone murders, well, there are still murders. Didn't work. Self-regulation is a nice idea, but human beings, as a rule, are not that good at it. We end up with kind of a mess.
God made a promise to Eve that one of her children would triumph over Satan. The nation of Israel is God keeping His promise to Eve. It's not that He didn't have anything to do with other nations, but He used Israel to bring the Messiah. And part of Israel's job was to stay pure.
They had a special relationship with Him and they had special rituals to remind them of their purity before Him. Not mixing their fabrics was to be a reminder that they were to be "unmixed" with idolatrous nations around them.
They were very rules oriented, because after all, that's what we wanted - to do it ourselves. And to do it ourselves, we have to know the rules. We have to know what God knows. God knows sin is horrific. That's what all the sacrifices are about.
Most of the rules that seem trivial are highly symbolic in nature.
When Jesus came, He saw that the rulers (the Scribes and the Pharisees) had even created rules on top of God's rules. They had ceremonial washings and took God's laws about Sabbath rest and made it so you couldn't pick fruit if you were hungry because they considered it work.
No matter how rule oriented we are, it still doesn't save us. It doesn't work.
Thinking we have to do it ourselves makes us a little neurotic, truth be told.
So we have grace. I don't believe, as some do, that grace means I can do whatever I want and Jesus makes it okay. But I do think it means that I strive to do what God wants me to do, knowing that He helps me and that Jesus is my advocate when I fail.
Because Jesus fulfilled the old law, those ceremonial laws don't apply to me. I can mix fabrics and eat lobster (I really like lobster, btw), without guilt. It's not the law I am under.
Since I'm not a Jew, the ten commandments don't apply to me. I know that seems like a shocking statement to most people. That doesn't mean I can murder or steal. Jesus reiterated and expounded upon 9 of the 10 commandments. But I don't keep the Passover or rest on Saturday, because I'm not an Israelite.
I don't think the cultural laws were trivial. They served a purpose. But they aren't binding today. What is binding to day deals with the human heart: loving God and treating others as we would be treated. To paraphrase what Jesus said, all other law hinges on those two principles.