Post cenam lente ambulatur, quia ambulatio brevis corpori salubris est.

Because post is a preposition that takes the accusative when it means after.

So:

• cena = dinner
• cenam = after dinner when used with post

This is very common in Latin:

• post cenam = after dinner
• post bellum = after the war
• post paucos dies = after a few days

So the accusative here is required by the preposition, not because cenam is a direct object.

Ambulatur is the 3rd person singular present passive form of ambulare.

Literally, it looks like is walked, but here it is being used as an impersonal passive, which is very common in Latin. In English we usually translate this kind of form as:

• one walks
• people walk
• there is walking

So lente ambulatur means something like:

• one walks slowly
• people walk slowly
• there is slow walking

It does not mean that some specific thing is being walked.

This is because Latin often uses the impersonal passive to express a general action without naming a subject.

English often uses:

• one
• people
• you in a general sense

Latin can instead use a passive verb in the 3rd person singular:

• pugnatur = people fight / there is fighting
• curritur = people run / there is running
• ambulatur = people walk / one walks

So this is a normal Latin way to make a general statement like After dinner, people walk slowly.

Because lente is an adverb, while lenta would be an adjective.

Here the sentence is describing how the walking happens:

• lente = slowly

It is modifying the verb ambulatur, not a noun.

Compare:

• vir lentus ambulat = the slow man walks
  
  • lentus describes vir
• vir lente ambulat = the man walks slowly
  
  • lente describes ambulat

So lente is correct because the sentence needs an adverb.

They come from the same root idea, but they are different parts of speech:

• ambulatur = a verb: one walks / people walk
• ambulatio = a noun: a walk, walking, a прогулation-like activity

In this sentence:

• ambulatur tells you that the action is happening
• ambulatio brevis names the activity itself: a short walk

So Latin is using both the verb and the related noun:

• Post cenam lente ambulatur = After dinner, people walk slowly
• quia ambulatio brevis corpori salubris est = because a short walk is healthy for the body

Because ambulatio brevis is the subject of est.

The phrase means:

• ambulatio = walk
• brevis = short

Since brevis describes ambulatio, it agrees with it in:

• case: nominative
• number: singular
• gender: feminine

So:

• ambulatio brevis = a short walk

They are nominative because this phrase is the thing being talked about in ambulatio brevis corpori salubris est.

Because salubris is a predicate adjective linked to ambulatio brevis by est.

In other words:

• ambulatio brevis = subject
• salubris est = is healthy / is beneficial

So salubris must agree with ambulatio:

• nominative
• singular
• feminine

This is just like:

• puella laeta est = the girl is happy
• ambulatio brevis salubris est = a short walk is healthy

Even though English uses healthy for the body, Latin keeps salubris in the nominative because it describes the subject, not corpori.

Corpori is the dative singular of corpus, meaning body.

Here it is used with salubris to mean:

• healthy for the body
• beneficial to the body

So:

• corpus = body
• corpori = to/for the body

This is a common use of the dative with adjectives that express suitability, advantage, usefulness, or harm.

So the structure is:

• ambulatio brevis corpori salubris est
• literally: a short walk is beneficial to the body

In strict English, healthy usually describes something that has health, while healthful describes something that promotes health. But in normal English, healthy is often used for both.

Latin salubris usually means:

• health-giving
• beneficial
• good for the health
• often simply healthy in translation

So here corpori salubris est means:

• is good for the body
• is beneficial to the body
• is healthy for the body

Because the verb is impersonal.

Latin does not need to say people or we here. The form ambulatur itself already gives the idea of a general, unnamed subject:

• one walks
• people walk

If Latin wanted to name a subject, it would normally use an active form instead, such as:

• homines lente ambulant = people walk slowly

But with ambulatur, the sentence stays more general and impersonal.

Quia means because and introduces a clause giving the reason.

So the sentence is in two parts:

1. Post cenam lente ambulatur
2. quia ambulatio brevis corpori salubris est

That means:

• After dinner, people walk slowly
• because a short walk is beneficial to the body

So quia connects the action with its explanation.

Latin word order is much more flexible than English word order because the endings show the grammatical relationships.

This sentence could be rearranged in several ways without changing the basic meaning, for example:

• Lente post cenam ambulatur, quia ambulatio brevis corpori salubris est.
• Post cenam ambulatur lente, quia corpori salubris est ambulatio brevis.

The original order is natural and clear:

• post cenam first sets the time
• lente comes before the verb and highlights the manner
• the reason clause follows after quia

So the word order helps emphasis and style, but the endings carry most of the grammar.

It is a standard prepositional phrase meaning after dinner, but it is also worth noticing that Latin often uses very simple time expressions like this without extra words.

English might say:

• after dinner
• after the meal
• once dinner is over

Latin can simply say:

• post cenam

So it is compact and idiomatic. A learner should get used to these short preposition + accusative time phrases.

Latin often uses either a noun or an infinitive, depending on the construction.

Here the sentence wants the idea a short walk as a concrete thing that can be described as beneficial. A noun phrase works very naturally:

• ambulatio brevis = a short walk

An infinitive like ambulare means to walk or walking in a more verbal sense. But brevis naturally describes a noun, so ambulatio brevis is the clearer choice for a short walk.

So Latin is treating the activity as a thing:

• a short walk is good for the body

rather than just the bare action to walk.