Learn Hardcore Polish: Mój brat jest chory, więc nie idzie do pracy. - My brother is sick, so he is not going to work.

In Polish, iść do pracy means to go to work (to the workplace), while pracować means to work (to perform work).
The sentence focuses on the fact that he is not going to his job/place of work, not on the fact that he is not working in general.
You could say …więc nie pracuje, but that would mean “…so he is not working”, which is a bit different in meaning.

Why is the verb idzie in the present tense if we are talking about today or the near future?

Polish often uses the present tense of motion verbs (like iść) to talk about the near future.
So nie idzie do pracy can naturally mean “he is not going to work (today / tomorrow, etc.)”.
If you want to stress the future more strongly, you can use nie pójdzie do pracy (simple future), which sounds a bit more like a decision, promise, or prediction: “he will not go to work.”

Why is it nie idzie and not idzie nie?

In standard Polish, the negative particle nie usually comes directly before the conjugated verb:

nie idzie, nie pracuje, nie mam.
The order idzie nie is incorrect here and would sound very unnatural.
So you should always say nie idzie, not idzie nie, in this kind of sentence.

What is the difference between nie idzie do pracy and nie chodzi do pracy?

Polish distinguishes between:

iść – movement at one specific time (one trip, one occasion),
chodzić – repeated, habitual movement (many times in general).

Nie idzie do pracy usually means “he is not going to work (this time / today).”
Nie chodzi do pracy means “he doesn’t go to work (at all / in general)”, which can suggest that he is unemployed, on long-term leave, retired, etc.
So in the context of being sick today, nie idzie do pracy is the natural choice.

Why is there a comma before więc?

Więc is a conjunction that connects two clauses, introducing a result: “so / therefore.”
In Polish, you must put a comma before więc when it links two full clauses, as in this sentence.
This is similar to writing in English: “My brother is ill, so he is not going to work.” – but in Polish the comma is obligatory, not optional.

Is the possessive mój necessary? Can I say Brat jest chory, więc nie idzie do pracy?

Yes, you can say Brat jest chory, więc nie idzie do pracy and it is perfectly correct.
With close family members (brat, siostra, mama, tata, etc.), Polish often omits the possessive when the context makes it clear whose relative it is.
Adding mój simply makes it explicit that you are talking about your brother; it can sound a bit more specific or emphasised: “My brother is ill…”

Why is it jest chory and not something like ma chorobę?

For a normal illness or being unwell, Polish almost always uses być + adjective, i.e. jest chory (he is ill).
The structure ma chorobę (he has a disease) is possible, but it sounds more medical or serious, like talking about a specific diagnosed condition.
For everyday sickness (a cold, flu, etc.), jest chory is the natural, standard way to say it.

Why does the adjective end in -y (chory) and not, for example, chora or chore?

Adjectives in Polish must agree with the noun in gender and number.

brat is masculine singular, so the adjective is chory.
Other examples:
moja siostra jest chora (siostra – feminine singular)
moje dzieci są chore (dzieci – plural)

So mój brat jest chory is masculine singular agreement and therefore correct.

Why is it do pracy and not do praca or do pracę?

The preposition do always requires the genitive case.
The noun praca in the nominative (dictionary form) changes to pracy in the genitive singular.
So:

nominative: praca
genitive: pracy
Therefore, do pracy (to work) is grammatically correct.

Can I change the word order in the second clause, for example to więc do pracy nie idzie?

Yes, you can say Mój brat jest chory, więc do pracy nie idzie.
This word order is also correct; it puts a bit more emphasis on do pracy (to work), like: “so to work he is not going.”
Polish word order is relatively flexible, but nie must still stay directly before idzie.
Some orders would sound unnatural, e.g. *więc nie do pracy idzie in this context.

Can I use dlatego instead of więc?

Yes. Another natural version is: Mój brat jest chory, dlatego nie idzie do pracy.
Both więc and dlatego express a result, but:

więc is closer to English “so”,
dlatego is closer to “therefore / that’s why.”

In everyday speech they are often interchangeable here; the main difference is nuance and style, not grammar.

Could I say …więc nie pracuje instead of …więc nie idzie do pracy?

You can, but it slightly changes the focus.

nie idzie do pracy focuses on not going to the workplace.
nie pracuje focuses on not working at all.

Mój brat jest chory, więc nie pracuje could suggest he is not working (maybe he’s on sick leave) without specifying whether he was supposed to go somewhere.
The original sentence specifically talks about not going to work.