I have faith in God "that it will happen just as he told me".

[sitifan]

So keep up your courage, men, for I have faith in God that it will happen just as he told me. (my bold)
https://biblehub.com/parallel/acts/27-25.htm
Is the clause in bold a noun clause or an adverb clause?

 

[Tarheel]

Well, it's not a noun clause, that's for sure. I wouldn't say it's an adverb clause either. I would just say it's a subordinate clause.

 

[Holmes]

So keep up your courage, men, for I have faith in God that it will happen just as he told me. (my bold)
https://biblehub.com/parallel/acts/27-25.htm
Is the clause in bold a noun clause or an adverb clause?

I believe that the clause in bold is an appositive clause (or whatever your preferred term is for such clauses). Here's my reasoning.

Faith is a noun which, like belief and certainty and knowledge, accepts appositive-clause complementation. For example:

I am here in the faith that it will happen just as he told me.

Should we be bothered by the fact that, in the have faith that construction, we don't have the definite article (the) before the noun (faith)?

I don't think so, for if we use the pseudo-cleft construction to isolate the article-free direct object, all continues to be well with the that-clause:

What I have is faith that it will happen just as he told me.

Further, we needn't worry about the prepositional phrase in God coming between faith and the appositive clause. This happens in other cases:

[His statement to me that he understood my answer] came as a relief.

 

[PaulMatthews]

So keep up your courage, men, for I have faith in God that it will happen just as he told me. (my bold)
https://biblehub.com/parallel/acts/27-25.htm
Is the clause in bold a noun clause or an adverb clause?

Preliminary point: I would avoid using the terms 'noun clause' and 'adverb clause' (and 'adjective clause'). The classification of finite subordinate clauses is based on their internal form rather than spurious analogies with the parts of speech.

The clause in bold is a declarative content clause functioning as complement of "faith in God".

Content clauses are the default kind of finite subordinate clause. As their name suggests, they are chosen simply for their semantic content.

 

[Holmes]

"appositive clause" (post #3) = "declarative content clause functioning as complement" (post #4)

Appositive clauses, or, as Paul Matthews calls them, declarative content clauses functioning as complements (syntacticians also call them "CP complements to N"), only work after certain nouns, usually after nouns that relate to verbs that take "that"-clause complements (statement, argument, thought, belief, proposal, assertion, vow, etc.), but also after nouns that relate to adjectives that accept such complements (necessity, possibility, likelihood, certainty, etc.), and after certain other nouns, too, such as faith.

 

[PaulMatthews]

So keep up your courage, men, for I have faith in God that it will happen just as he told me.

To repeat my previous comment, declarative content clauses are the default kind of finite subordinate clause.

The fact that in some cases a that clause licensed by a noun does entail an appropriate content clause is attributable to the semantic properties of the noun: it is not a systematic feature of the noun + content clause construction.

It is a requirement of appositive modifiers (and supplements) that they can be substituted for the whole NP, but in your example, replacing the NP "faith in God" with the content clause in bold results in loss of grammaticality.

For those reasons, the content clause in bold does not satisfy the condition for analysis as an appositional construction. It is simply a declarative content clause functioning as complement of "faith in God".

 

[Holmes]

To repeat, "appositive clause" is a term from traditional grammar which picks out exactly the same thing Paul Matthews's fancier jargon picks out here.

 

[PaulMatthews]

There is no evidence to support a claim that declarative content clauses can systematically function as appositives.

In my experience, many (perhaps most) resources say that appositives consist of noun phrases.

Note also my earlier comment that "that it will happen just as he told me" cannot replace "faith in God" without loss of grammaticality.