What was Eru's message? Harmonize.
This, to me, translates into living in accord with others. We today in RL think the same, and have laws (whether God-given or society-evolved) that show us what 'good' conduct is.
You know, thou shalt not murder, steal, etc.
Why? Because as individuals, we are vulnerable. I think about this every time I'm sent somewhere alone where everyone speaks a foreign tongue. I spend days 'inside my own head,' and it isn't fun. Add to this, having one to watch one's back, help gathering food, maintaining shelter, raising a family, caring for the tribe.
Our survivability increases with numbers, but so does the possibility of conflict. And so some basic rules.
In the beginning, all were in harmony, then Melkor, and a few others like him, decided that his part was more important than the survival of the group. Sure, he might gain, but the group lost (and some even grew silent). Eru raised up other themes to counter this 'it's all about me-ism' of Melkor's. In the end, Melkor never finds the Imperishable Flame, as he's too self-centered, and ends in the Void. Those that follow Eru, live in accord, find something more at the end of the music.
Turin and Tuor: Turin, though never as selfish as Melkor, makes life all about himself, whereas Tuor follows another tune, and brings about a better day for many.
And in LotR, isn't not all about Frodo, or Aragorn, or Gandalf, but their selfless relationships with others (Sam, Faramir, Eomer, the Fellowship, etc).
Okay, so that was a little rambling.
