Sem revisar a gramática, fica difícil escrever uma redação clara.

In Portuguese, sem can be followed by an infinitive to mean without doing something.

• sem = without
• revisar = to review / to check

So:

• Sem revisar a gramática = Without reviewing the grammar

This is a very common structure in Portuguese:

• Sem estudar, fica difícil passar. = Without studying, it becomes hard to pass.
• Sem dormir bem, fica difícil trabalhar. = Without sleeping well, it becomes hard to work.

After sem, Portuguese usually uses the infinitive, not the gerund, when you mean without doing something in a general way.

So the natural form is:

• sem revisar

not usually:

• sem revisando

For an English speaker, it may feel like without reviewing should use a form like reviewing, but Portuguese works differently here. The infinitive is the normal choice.

Literally, fica difícil means something like becomes difficult or gets difficult.

In this sentence, though, it is best understood as:

• it becomes difficult
• or more naturally in English, it’s hard

So:

• Sem revisar a gramática, fica difícil escrever uma redação clara.

has the sense of:

• Without reviewing grammar, it’s hard to write a clear essay/composition.

Portuguese often uses ficar + adjective to show that something ends up in a certain state because of some condition.

This is an impersonal-style structure. Portuguese often says:

• É difícil estudar.
• Fica difícil entender.
• Vai ser fácil resolver isso.

English usually needs it:

• It is difficult to study
• It becomes hard to understand

Portuguese often does not use an equivalent visible subject here. The real idea being discussed is the infinitive phrase:

• escrever uma redação clara

So the sentence is basically structured like:

• Without reviewing grammar, [it] becomes difficult to write a clear composition.

The it is not expressed.

Both are possible, but they are slightly different in feel.

• é difícil = is difficult
• fica difícil = becomes difficult / ends up being difficult

In this sentence, fica difícil suggests that because of the lack of review, the task becomes hard. It emphasizes the result of that condition.

Compare:

• É difícil escrever uma redação clara. = Writing a clear composition is difficult.
• Sem revisar a gramática, fica difícil escrever uma redação clara. = Without reviewing grammar, it becomes difficult to write a clear composition.

So fica adds a sense of consequence.

Because Sem revisar a gramática is an introductory phrase placed before the main clause.

The comma helps separate:

• the condition/circumstance: Sem revisar a gramática
• from the main statement: fica difícil escrever uma redação clara

This is very natural punctuation in Portuguese. You may sometimes see short introductory phrases without a comma, but here the comma is standard and clear.

Portuguese uses the definite article much more often than English, especially with general nouns.

So:

• revisar a gramática

is very natural, even if English would often just say:

• review grammar

In Portuguese, the article often appears where English omits it.

Other examples:

• Estudo o português todos os dias. = I study Portuguese every day.
• Ela adora a música brasileira. = She loves Brazilian music.

Here, revisar means to review, to check over, or to go back and look at carefully.

In context, revisar a gramática suggests checking grammar rules or reviewing grammatical accuracy before writing.

Depending on context, revisar can also mean:

• review notes
• proofread
• check for errors
• go over something again

So here it is not just memorizing grammar in general; it suggests actively checking or reviewing grammar.

Because clara is describing the noun redação.

• uma redação clara = a clear composition

This is the most natural way to say that the text itself is clear.

If you say:

• escrever claramente

that means to write clearly, focusing more on the manner of writing.

So the two ideas are related, but not identical:

• escrever uma redação clara = write a clear composition
• escrever claramente = write clearly

In Portuguese, adjectives often come after the noun.

So:

• redação clara = clear composition
• livro interessante = interesting book
• explicação simples = simple explanation

Some adjectives can come before the noun, but after the noun is the default and most neutral position.

Because adjectives must agree with the noun they describe.

• redação is feminine singular
• so the adjective must also be feminine singular: clara

Compare:

• um texto claro = a clear text
• uma redação clara = a clear composition
• textos claros = clear texts
• redações claras = clear compositions

Redação can mean composition, essay, or written text, depending on context.

For learners, essay is often a good translation, but redação is a bit broader. In Brazilian Portuguese, it is very common in school contexts for a written assignment or composition.

Some related words:

• redação = composition / essay
• texto = text
• ensaio = essay, but often more formal/literary depending on context

So in this sentence, redação likely means a school-style written composition.

Because difícil can be followed directly by an infinitive in Portuguese.

So these are normal:

• É difícil entender. = It is difficult to understand.
• Fica difícil escrever bem. = It becomes hard to write well.

You do not need para here.

Sometimes Portuguese does use para with infinitives, but after expressions like é difícil or fica difícil, the direct infinitive is very common and natural.

Yes. That would also be correct.

The difference is mainly nuance:

• é difícil = states a general difficulty
• fica difícil = suggests that under those circumstances, it becomes difficult

So:

• Sem revisar a gramática, é difícil escrever uma redação clara.
• Sem revisar a gramática, fica difícil escrever uma redação clara.

Both work, but fica difícil sounds a little more connected to the consequence of not reviewing grammar.

Yes. In context, it means something like:

• if you don’t review the grammar first
• or without reviewing grammar beforehand

Portuguese does not need to say antes here, because the sequence is already understood from the meaning.

If you wanted to make it more explicit, you could say:

• Sem revisar a gramática antes, fica difícil escrever uma redação clara.

But the original sentence already sounds complete and natural.