هذه الكنيسة قديمة.

Because الكنيسة is a feminine singular noun in Arabic, and the demonstrative has to match it.

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

So:

• هذا الكتاب = this book
• هذه الكنيسة = this church

Even though a church is not biologically female, nouns in Arabic still have grammatical gender.

A careful MSA pronunciation is:

hādhihi al-kanīsatu qadīmatun

If you read it without full case endings, as learners often do, you will commonly hear:

hādhihi al-kanīsa qadīma

A quick breakdown:

• هذه = hādhihi
• الكنيسة = al-kanīsa
• قديمة = qadīma

Also note:

• In الكنيسة, the l in الـ is pronounced, because ك is a moon letter, not a sun letter.
• So it is al-kanīsa, not ak-kanīsa.

In Arabic, the present tense of to be is usually not stated in simple sentences like this.

So:

• هذه الكنيسة قديمة literally looks like this church old
• but it means This church is old

This is called a nominal sentence in Arabic.

If you wanted past tense, then Arabic would use a verb, for example:

• كانت هذه الكنيسة قديمة = This church was old

Because الكنيسة is the noun the church, while قديمة is the predicate adjective old.

In this sentence:

• هذه الكنيسة = this church
• قديمة = is old

So قديمة is not being used like the old church. It is describing the church as the predicate of the sentence.

Compare:

• هذه الكنيسة قديمة = This church is old
• هذه الكنيسة القديمة = This old church

In the second sentence, القديمة is an attributive adjective directly modifying الكنيسة, so it becomes definite too.

It is an adjective in meaning, but in the structure of the sentence it functions as the predicate.

Arabic grammar often distinguishes between:

• an adjective that directly modifies a noun
• an adjective used as the predicate in a sentence

Here:

• الكنيسة القديمة = the old church
  Here القديمة directly modifies الكنيسة.

But:

• الكنيسة قديمة = the church is old
  Here قديمة is the predicate: it tells you something about the church.

So yes, it is an adjective, but grammatically it is the predicate adjective.

Because it is the feminine singular form of the adjective.

The basic masculine form is:

• قديم = old

The feminine form is:

• قديمة = old

Since الكنيسة is feminine singular, the adjective must agree with it:

• كنيسة قديمة = an old church
• الكنيسة قديمة = the church is old

This is a very common pattern in Arabic: many feminine nouns and adjectives end in ة.

Yes. In Arabic, adjectives agree with the noun they describe in:

• gender
• number
• definiteness
• and usually case

Here:

• الكنيسة = feminine singular
• قديمة = feminine singular

So they match.

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

• هذا المسجد قديم = This mosque is old

If it were feminine:

• هذه الكنيسة قديمة = This church is old

With full case endings, the sentence is:

هٰذِهِ الْكَنِيسَةُ قَدِيمَةٌ

Transliteration:

hādhihi al-kanīsatu qadīmatun

Why?

• الكنيسةُ is the subject of the nominal sentence, so it is nominative
• قديمةٌ is the predicate, so it is also nominative

In everyday speech and in much unvocalized writing, these endings are often not pronounced clearly, but in formal grammar they are there.

That is also possible, but it means something slightly different.

• هذه الكنيسة قديمة = This church is old
• هذه كنيسة قديمة = This is an old church

In the first sentence, الكنيسة is definite: you are talking about this specific church.

In the second, كنيسة قديمة is indefinite: you are saying this is an old church.

So the presence or absence of الـ changes the structure and meaning.

With a demonstrative like هذا / هذه, it is very common in MSA to have:

demonstrative + noun

So:

• هذه الكنيسة = this church
• هذا البيت = this house

This is the normal order for a phrase like this church.

Arabic word order is flexible in some contexts, especially in full sentences, but in a basic demonstrative phrase, this order is standard.

Yes, الكنيسة is grammatically feminine.

One clue is the ending ة (tāʾ marbūṭa), which very often marks feminine nouns:

• كنيسة = church
• مدينة = city
• سيارة = car

Not every feminine noun ends this way, and not every noun ending in ة is interpreted exactly the same way in all contexts, but it is a very strong and common clue.

Because الكنيسة is feminine, it takes:

• هذه not هذا
• قديمة not قديم

A masculine version would use:

• هذا instead of هذه
• a masculine adjective such as قديم instead of قديمة

For example:

• هذا المسجد قديم = This mosque is old
• هذا البيت قديم = This house is old

So the pattern is:

• feminine: هذه الكنيسة قديمة
• masculine: هذا ... قديم

In careful MSA, it is hādhihi.

In some real-life pronunciation, especially outside very careful reading, speakers may pronounce it more lightly, but for learning MSA you should aim for:

• هٰذِهِ = hādhihi

That is the safe and standard form to learn first.

No. هذه الكنيسة قديمة means This church is old, not This old church.

To say this old church, you would say:

هذه الكنيسة القديمة

Here, القديمة directly modifies الكنيسة, so it must also be definite.

So compare:

• هذه الكنيسة قديمة = This church is old
• هذه الكنيسة القديمة = This old church

That difference is very important in Arabic.