You've come to this page because you've said something similar to:
I cannot tell what you were replying to from the quote that you gave.
This is the Frequently Given Answer to such requests.
Minimalism in quoting is a very good thing, recommended in so many places — from Learn To Quote (which has an English language equivalent), that in fact briefly alludes to people doing as common practice exactly what this page tells you to do, to the Google Groups posting style guide — that it is impossible to list them all here. Quoting is not there to tell you what message was being replied to. The standard message format already has a mechanism for this.
That mechanism is the standard References: header that is supplied in the message. Use it. It provides you with exactly what message is being replied to. Indeed, it provides you with a chain of messages, so you can track back a fair way along the thread, often as far as the message that began it.
So if you want more context than what has been given, use a modicum of initiative. Use the content of the References: header to find the message that was replied to, and read it. Stop expecting the rest of us to waste everyone's time, storage space, and bandwidth by quoting massive portions of messages.
Some message reader softwares make using the References: header dead easy. Netscape Communicator, for example, displays the References: header as a series of hyperlinks, which lead directly to each of the messages listed in the header. Finding the message being replied to takes a single mouse click.
Navigation of message threads based upon the References: header has been a standard feature of message readers since the 1980s. (The mechanism itself dates from the early 1980s. You can see it documented in § 2.2.6 of RFC 850, published in 1983, for example.) If your message reader does not provide the ability to travel a thread based upon the References: header, then you should contact its author pronto.
Do not complain that you cannot find referenced messages by ID because
your NNTP server's expiration policy is such that the original message
has been deleted from its database. First: One can retrieve Usenet
messages by their message IDs from
DejaNewsGoogle.
Second: Quite a few major Usenet carriers nowadays have pretty much
stopped expiring messages in text newsgroups altogether. (Highwinds
Media as of 2010, for example, carries all text newsgroup traffic back to
2005.)