the expression of "having (a/the/) belief (in/that)...?"

You have a non-standard comparison here, because both "religion" and "a religion" be used in these three sentences. Simply using "religion" makes them general questions or statements. Using "a religion" is still imprecise, but implies a particular confession, a particular established religion.

The first sentence lacks a necessary preposition. It ought to read: "Do you agree that having belief in a religion is helpful to one's life?" Even then, it is awkward. A better rendering would be: "Do you agree that having a belief in a religion is helpful in one's life." In any of these examples, either "a religion," or simply "religion" can be used.

The distinction here is subtle. "A religion" immediately implies participation in an existant, established religious confession--such as being a Presbyterian, or a Jain, or an Orthodox Jew, or a Sunni Muslim. "Religion" by itself, with no indefinite article, can simply mean a religious belief in anything, and does not necessarily imply participation in an established, organized religious confession. So someone might believe in religion--as in being a Christian, for example--without being a member of an organized religious confession.

I saw three sentences like below:

I saw three sentences like the ones below:

Or

I saw three sentences like these below:

Is these are all correct?

Are these all correct?

"These" is plural. Therefore, for the subject and the verb to agree in number, the form of the verb to be which you must use is "are." You cannot use both "is" and "are" in the sentence, you need one or the other, and in this case, you need "are."

have a belief / have the belief / have belief

have a belief or have belief are acceptable. have the belief is not acceptable. If you wished to use "have the belief" you would need to follow it with "that": I have the belief that a religion is helpful to one's life. Finally, it would be more common in English to say "helpful in one's life," rather than "helpful to one's life."

And I think the last sentence, I agree that having religion ..., needs OBJECT after 'having', right?

". . . needs an object after "having," right?"

Yes, and "religion" is that object.





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