How we cite our quotes: (Chapter.Paragraph)
Quote #4
"Sir, I honor and respect the personal dignity of any man who respects my dignity. I am indeed indebted to you. And I always pay my debts. If it is your custom that this knife remain sheathed here, then it is so ordered—by me. And if there is any other way we may honor the man who died in our service, you have but to name it." (12.145)
Leto honors the tradition and customs of another culture because it's the polite and respectful thing to do. Also, he probably doesn't want to kill anyone.
Quote #5
It was the custom, the housekeeper had explained, for guests as they entered to dip their hands ceremoniously into a basin, slop several cups of water onto the floor, dry their hands on a towel and fling the towel into the growing puddle at the door. After the dinner, beggars gathered outside to get the water squeezing from the towels. […] "The custom stops here!" [Leto] muttered. (15.7-9)
Then again, sometimes traditions and customs just need to change. These two examples are pretty clear-cut, but in real life, the line between traditions that need altering and those that don't can get super tricky. Case in point: the way Americans argue over the Second Amendment.
Quote #6
Kynes shook his head, spoke in a lecturing tone: "Not the blood, sir. But all of a man's water, ultimately, belongs to his people—to his tribe. It's a necessity when you live near the Great Flat. All water's precious there, and the human body is composed of some seventy per cent water by weight. A dead man, surely, no longer requires that water." (16.147)
If you want to know what a culture values most, look at their funeral traditions and customs. The way a culture treats its dead will tell you everything you need to know about its values.