What is the purpose of colon ":" in this sentence "everyone: and reason"? "The state of nature has a law of nature to govern it, which obliges every one: and reason, which is that law, teaches all mankind, who will but consult it, that, being all equal and independent, no one ought to harm another in his life, health, liberty, or possessions."
The sentence you're asking about appears to be from an 18th-century document, and conforms to 18th-century practices, such as using a colon to nearly but not quite end a sentence; and using lots of commas where we would not these days--not to mention what we would consider a rather convoluted word order. I would render the sentence in more modern prose as something like this:
"[The state of] Nature is governed by a law which applies to everyone. That law is Reason, which teaches all mankind--or at least all of mankind that trouble themselves to consult it--that, since all members of mankind are equal and independent, no one should harm another's life, health, liberty, or property."
My version reads more like late-19th or early- to mid-20th century prose. I present it as an example, not as anything definitive. Note that I replaced the colon after "everyone" with a period/full stop, and replaced the commas before and after "who will but consult it" with dashes.