هذه خطوة مهمة.

A careful MSA pronunciation is:

hādhihi khuṭwatun muhimmatun

In normal pause at the end of the sentence, the case endings are usually not pronounced, so you will often hear something closer to:

hādhihi khuṭwa muhimma

A few notes:

• هذه = hādhihi
• خطوة = khuṭwa
• مهمة = muhimma

The letter ط in خطوة is an emphatic t, heavier than ordinary ت.

Because خطوة is a feminine noun.

In MSA, demonstratives must agree with the noun in gender:

• هذا = this for masculine nouns
• هذه = this for feminine nouns

Since خطوة means step and is feminine, you say:

• هذه خطوة

not

• هذا خطوة

A big clue is the ending ة (called tāʾ marbūṭa). This ending often marks feminine nouns.

So:

• خطوة = a feminine noun
• مهمة also has ة, because it is the feminine form of the adjective important

This is why both the demonstrative and the adjective are feminine here.

In Arabic, the verb to be is usually not expressed in the present tense.

So instead of saying:

• This is an important step

Arabic simply says:

• هذه خطوة مهمة

Literally, it is more like:

• This important step

but the meaning is naturally understood as This is an important step.

If you wanted the past or future, Arabic would use a verb:

• كانت هذه خطوة مهمة = This was an important step
• ستكون هذه خطوة مهمة = This will be an important step

In Arabic, adjectives normally come after the noun they describe.

So:

• خطوة مهمة = an important step

Word-for-word:

• خطوة = step
• مهمة = important

This is the normal Arabic order:

• noun + adjective

not the English order:

• adjective + noun

Because Arabic adjectives must agree with the nouns they describe.

They usually match in:

• gender
• number
• definiteness
• and, in fully vowelled Arabic, case

Since خطوة is feminine singular, the adjective must also be feminine singular:

• خطوة مهمة = feminine noun + feminine adjective

If the noun were masculine, you would use the masculine form of the adjective:

• هذا أمر مهم = This is an important matter

Because the sentence means This is an important step, not This is the important step.

• خطوة = a step
• الخطوة = the step

So:

• هذه خطوة مهمة = This is an important step
• هذه الخطوة المهمة would mean something different, more like this important step
• هذه الخطوة مهمة means This step is important

That last one is especially useful to compare:

• هذه خطوة مهمة = This is an important step
• هذه الخطوة مهمة = This step is important

This is a nominal sentence in Arabic.

A simple way to analyze it is:

• هذه = the topic / subject-like element
• خطوة مهمة = the predicate / what is being said about it

So the structure is:

• هذه
  • خطوة مهمة
• This
  • an important step

In traditional grammar terms, هذه is the مبتدأ and خطوة مهمة is the خبر.

The final ة (tāʾ marbūṭa) has two common pronunciation patterns:

1. At pause (when you stop on the word), it is usually pronounced like -a / -ah

   • خطوة → khuṭwa
   • مهمة → muhimma

2. When grammatical endings are pronounced, it behaves like a t

   • خطوةٌ → khuṭwatun
   • مهمةٌ → muhimmatun

That is why dictionaries may show forms that seem slightly different from what you hear in normal speech.

In fully vowelled formal MSA, the sentence would typically be:

هٰذِهِ خُطْوَةٌ مُهِمَّةٌ

And it can be read as:

hādhihi khuṭwatun muhimmatun

Why -un on both words?

• خطوةٌ is the predicate and is indefinite, so it takes tanwīn
• مهمةٌ is an adjective describing خطوة, so it matches it

In everyday reading and most speech, these endings are usually omitted.

Yes, and it is very natural, but the meaning changes slightly.

Compare:

• هذه خطوة مهمة = This is an important step
• هذه الخطوة مهمة = This step is important

The first introduces or identifies something as an important step.

The second talks about this specific step and says that it is important.

Good question. Arabic allows both patterns, but they are not exactly the same.

1. Demonstrative + definite noun

   • هذه الخطوة = this step

2. Demonstrative used in a full sentence

   • هذه خطوة مهمة = This is an important step

So in your sentence, هذه is not simply part of a noun phrase like this step. It is functioning as the start of a complete sentence.

Yes. هذه خطوة مهمة is fully natural and idiomatic in MSA.

It is the kind of sentence you might see in:

• news writing
• formal speeches
• essays
• textbooks
• professional discussion

It is a very useful model sentence because it shows several core MSA patterns at once:

• demonstrative agreement
• omitted present-tense to be
• noun + adjective order
• adjective agreement