(Passive clause) We learn language when messages being communicated are compelling.
We learn language when messages are communicating are compelling .
Is the 2 sentence correct ? Why use verb 'are' here I mean it is just a statement not a state, it is not happening right now. Is it a universal truth(atleast for the speaker) ?
As James mentioned, sentence 2 is not grammatically correct, because you've got too many (finite) verbs for one subject. However, I think part of the problem here is a larger confusion between passive clauses and passive sentences. There are some things you can do with passive sentences that you really cannot do with clauses, because they would require rearranging things that are important to the larger sentence.
In this case, it's important to note that "being communicated" is a modifier of "messages". We can remove that clause and the sentence still makes sense (although it's a little less specific):
We learn language when messages are compelling.
Now you say you want to change "messages being communicated" into an active voice. Well, there are a couple of problems here. Let's forget for a moment that this is a clause in the middle of a sentence and just pretend we're dealing with a simple sentence on its own:
Messages are being communicated. (passive voice)
First of all, we don't actually have enough information here to change this to active voice (without adding something). In order to make it active, we would need to know what is doing the communicating, so if we had something like:
Messages are being communicated by people. (still passive)
Then we could make that active by switching the nouns around:
People are communicating messages. (active voice)
But with "Messages are being communicated", we're just left with:
___ are communicating messages. (???)
..which isn't a valid sentence (or clause) on its own.
Ok, so instead let's pretend we do have enough to work with. Maybe the original sentence was actually:
We learn language when messages being communicated by people are compelling.
Ok, so now we can switch that clause around to active voice, right? Well, no, because we have to think of the larger sentence:
We learn language when messages (...) are compelling.
Here, "messages" needs to be in a position to be the subject of "are compelling" in order for everything to make sense. But if we switch the phrase around to active voice we're also swapping the position of "messages" and "people", so you end up with:
We learn language when people communicating messages are compelling. (wrong)
This is actually grammatically correct, but now we've changed the meaning of the larger sentence. It went from:
We learn language when (certain types of) messages are compelling.
to
We learn language when (certain types of) people are compelling.
Which is really not the same thing.
So this is a situation where passive and active voice just really aren't interchangeable, because the passive voice has to be used to make sure the right word is the subject in the larger sentence.
As a side note, the original sentence is technically grammatically correct, but would probably be better phrased (and easier for the reader to understand) as either:
We learn language when the messages being communicated are compelling.
or:
We learn language when messages which are being communicated are compelling.
Sentence 2 is incorrect and not grammatical English.
There are two finite verbs for the subject "messages", and that is not allowed.
The first problem is "messages are communicating". A message can't communicate, only people can communicate. When the grammar is wrong, we can often understand the meaning from the rest of the sentence. But here the meaning is weird, and the result is that the second sentence makes no sense.
A natural way to rephrase would be "... when compelling messages are communicated"
