Puella dicit se hoc beneficium memoria semper servaturam esse.

Because se is the reflexive pronoun. It refers back to the subject of the main clause, here puella.

So in:

• Puella dicit = The girl says
• se ... servaturam esse = that she will preserve/keep ...

Latin uses se when the subject inside the reported statement is the same person as the subject of the main verb.

If you used eam, that would normally mean her as someone else, not the girl herself.

Because this sentence uses indirect statement, also called the accusative-and-infinitive construction.

After verbs like dicit (says), Latin often does not use that + a finite verb the way English does. Instead, it uses:

• a subject in the accusative
• plus an infinitive

So:

• se = accusative subject of the infinitive
• servaturam esse = infinitive phrase

Literally, Latin is doing something like:

• The girl says herself to be going to keep ...

That is just how Latin expresses The girl says that she will keep ...

Because Latin needs a future infinitive here.

The main verb is dicit = says, and the action of keeping the favor is still in the future relative to that speaking. So Latin uses:

• future active participle
  • esse
• here: servaturam esse

This means to be going to keep or simply will keep in indirect statement.

A useful comparison:

• servare = to keep, often for action happening at the same time as the main verb
• servaturam esse = to be going to keep, for action later than the main verb

So Latin is carefully showing the time relationship.

Because it agrees with se, which refers to puella, a feminine singular person, and se is accusative because of indirect statement.

So servaturam is:

• feminine
• singular
• accusative

It must match the understood person who will do the action.

If the subject were a boy, you would get:

• servaturum esse

If it were plural girls:

• servaturas esse

Esse is part of the future infinitive.

Latin forms the future infinitive actively as:

• future participle + esse

So:

• servaturam esse = to be about to keep / to be going to keep

Without esse, the construction would be incomplete.

It is the direct object of servaturam esse.

The verb servare takes an object: you keep or preserve something. Here that something is:

• hoc beneficium = this kindness/favor/benefit

Both words are accusative singular neuter:

• hoc = this
• beneficium = kindness, favor, benefit

So the structure is:

• se = subject of the infinitive
• hoc beneficium = object of the infinitive
• servaturam esse = infinitive verb phrase

Because the sentence needs a direct object, not possession.

The girl is not saying something about this favor’s memory or of this favor. She is saying that she will keep this favor in memory.

So Latin uses the accusative direct object:

• hoc beneficium

Genitive forms such as huius beneficii would mean of this favor, which is not the role needed here.

This is an idiomatic use. Latin can use memoria in the ablative with verbs of remembering or preserving in memory, in the sense of:

• in memory
• by memory
• as a matter of remembrance

So memoria servare means something like to keep in memory or to preserve in remembrance.

English often wants a preposition, as in in memory, but Latin does not always need one.

Because Latin often expresses ideas that English uses a preposition for by using a bare case ending instead.

Here the ablative memoria can convey the idea without in.

So Latin says:

• memoria servare

where English naturally says:

• keep in memory
• remember

That is a normal difference between the languages.

Not as a completely frozen phrase, but it is built from very natural Latin patterns.

The important part is the combination of:

• a verb like servare
• plus memoria

to express preserving something in one’s memory.

So a learner should recognize the idea as idiomatic Latin, even if the exact wording is not the only possible way to say it.

It goes with servaturam esse, not with dicit.

So the meaning is:

• she says that she will always keep this favor in memory

not:

• she always says that she will keep this favor in memory

Latin word order is flexible, but here semper is naturally understood with the infinitive phrase that follows.

Yes. Latin word order is much freer than English word order because the endings show the grammatical roles.

For example, the following would still mean basically the same thing:

• Puella se hoc beneficium memoria semper servaturam esse dicit.
• Puella dicit hoc beneficium se memoria semper servaturam esse.

However, word order can affect emphasis. The given order is perfectly normal and clear.

Because in Latin, after verbs of saying, thinking, knowing, hearing, and so on, the usual construction is indirect statement, not that + finite clause.

So English says:

• The girl says that she will keep this favor in memory

But Latin says:

• Puella dicit se hoc beneficium memoria semper servaturam esse

with accusative + infinitive instead of a separate that-clause.

Because hoc beneficium is already the natural direct object of servare, and because in an indirect statement the accusative pronoun usually serves as the subject of the infinitive.

So the roles are:

• se = the one who will keep
• hoc beneficium = the thing being kept in memory

Also, servaturam is feminine singular accusative, which matches se referring to puella. That agreement shows that se is the subject of the infinitive.

Dicit is present tense: she says.

Because the speaking is present, the future infinitive servaturam esse shows an action that is still future relative to that present speaking.

So the time relationship is:

• dicit = now she says
• servaturam esse = later she will keep/preserve

This is one of the key things Latin infinitives in indirect statement help express.

Then Latin would probably use a present infinitive instead of a future infinitive.

For example, if the meaning were:

• The girl says that she keeps this favor in memory

Latin could use something like:

• Puella dicit se hoc beneficium memoria servare.

But in your sentence, the future idea is important, so Latin uses:

• servaturam esse

Any of those can fit depending on context.

For a learner, the important thing grammatically is that beneficium is the thing being remembered. In many contexts it means:

• a kindness
• a favor
• a service done for someone
• a benefit

So the sentence implies gratitude: the girl says she will not forget the good turn done for her.

Because Latin relies much more on:

• case endings
• infinitive constructions
• participles

English more often relies on:

• fixed word order
• helper words like that
• finite verb forms

So a sentence like this can feel strange at first, but it follows very regular Latin patterns:

1. dicit introduces reported speech
2. se gives the subject of the reported statement
3. servaturam esse expresses future action in that statement
4. hoc beneficium is the object
5. memoria shows the idea of keeping something in memory

Once you learn the accusative-and-infinitive pattern, this kind of sentence becomes much easier to read.