В этом суть проблемы.

Russian usually omits the present-tense form of to be in sentences like this.

So:

• В этом суть проблемы. literally works like
• In this — the essence of the problem.

In natural English, we supply is:

• That is the essence of the problem
• That’s the crux of the problem

If you want extra emphasis in Russian, you can sometimes add и есть:

• В этом и есть суть проблемы.
  = That is exactly the essence of the problem.

But in the basic sentence, no verb is needed.

В этом literally means in this or in that.

In this sentence, it is used idiomatically to mean something like:

• that’s where it lies
• that’s the point
• that’s the crux

So В этом суть проблемы is not just a physical in this. It means:

• This is the heart of the problem
• That’s exactly what the problem is
• That’s the essence of the problem

It points to something previously mentioned or understood from context.

Because the preposition в requires a case, and here it takes the prepositional case.

• это = the basic dictionary form, this / it
• в этом = in this / in that

So the form changes because of the preposition:

• это
• в этом

This is a very common pattern in Russian:

• в доме = in the house
• в книге = in the book
• в этом = in this

Here, суть is a noun, not a verb.

It means:

• essence
• core
• substance
• crux

So:

• суть проблемы = the essence of the problem / the crux of the problem

A learner may be confused because суть can also look like an old or formal verb form related to быть in some contexts, but in this sentence it is clearly the noun essence.

Because суть usually takes the genitive case: the essence of what?

So:

• суть чего? = the essence of what?
• суть проблемы = the essence of the problem

That is why проблема changes to проблемы.

More examples:

• суть вопроса = the essence of the question
• суть дела = the essence of the matter
• суть конфликта = the essence of the conflict

Yes, it is completely natural.

It sounds fairly neutral and is often used in speech and writing when someone is identifying the key issue.

Depending on context, good English equivalents are:

• That’s the crux of the problem
• That’s the heart of the problem
• That’s the whole point of the problem
• That’s where the problem lies

It can sound a bit thoughtful or explanatory, but not unnatural or overly formal.

Yes. Russian word order is flexible, and changing it changes the emphasis.

Compare:

• В этом суть проблемы.
  Emphasis on this: That’s the essence of the problem.

• Суть проблемы в этом.
  Emphasis on the essence of the problem first, then the explanation: The essence of the problem is this.

Both are grammatical and natural. The difference is mainly stylistic and informational: what comes first is often what the speaker wants to frame as the topic.

Usually, that would sound less natural in this meaning.

Russian prefers В этом суть проблемы or Суть проблемы в этом when expressing that’s the crux of the problem.

Why? Because the idea is not simply this equals the essence of the problem, but rather the essence of the problem lies in this.

So the most idiomatic versions are:

• В этом суть проблемы
• Суть проблемы в этом

They are related, but not identical.

• суть = essence, core, crux
• смысл = meaning, sense, point

In many contexts they overlap, but суть is usually about the inner nature or core of something, while смысл is often about meaning or purpose.

Compare:

• В этом суть проблемы.
  = That’s the essence/crux of the problem.

• В чём смысл?
  = What’s the point? / What’s the meaning?

If you used смысл here, it would change the nuance.

A simple pronunciation guide is:

• В этом суть проблемы
• v EH-təm sootʹ prə-BLYE-mɨ

A few notes:

• в этом: the в is pronounced like v
• этом: stress is on the first syllable
• суть: the final ь softens the т
• проблемы: stress is on бле → проблЕмы

So the strongest stress in the sentence usually falls on:

• Э in этом
• БЛЕ in проблемы

It very often refers to something just mentioned.

For example:

• Люди не слушают друг друга. В этом суть проблемы.
  = People don’t listen to each other. That’s the crux of the problem.

So в этом often means:

• in this fact
• in this situation
• in what I just said

It does not have to be literal or physical. It is commonly used to point back to an idea, explanation, or argument.