Learn Hardcore Spanish (Spain): Mi primo asegura que el pasillo será más seguro después de decorar las paredes. - My cousin assures that the hallway will be safer after we decorate the walls.

It literally means "My cousin assures (that)". Here asegurar doesn’t mean “to ensure” (garantizar) but rather “to state/claim/assert” something. A natural translation would be:

“My cousin claims that…”
“My cousin says that…”
“My cousin assures (me) that…”

Why is there a que after asegura?

Because asegurar used with a subordinate clause requires the conjunction que to introduce what is being asserted. The pattern is:

asegura que + [clause]
Just like English “claims that,” “says that,” etc. Without que, the sentence would be incomplete.

Why is será used instead of es?

Será is the simple future of ser (“to be”). The speaker isn’t describing a current fact but predicting a future condition:

es más seguro = “it is safer” (now)
será más seguro = “it will be safer” (later, after the walls are decorated)

Could we use va a ser instead of será? If so, is there any nuance?

Yes. Va a ser más seguro uses the periphrastic future and is very common in spoken Spanish, expressing a planned or likely outcome based on current information. Será más seguro (simple future) often sounds a bit more formal or expresses a firmer prediction. Both mean “it will be safer.”

Why does the sentence say después de decorar las paredes instead of using a conjugated verb?

Because después de is a preposition, and prepositions must be followed by a noun or an infinitive, never a finite verb. Therefore you say:

después de decorar las paredes (“after decorating the walls”)

If you want a full clause with a conjugated verb you must add que + subjunctive:

después de que decoremos las paredes

Could you shorten decorar las paredes by using a pronoun?

Absolutely. You can attach the object pronoun to the infinitive:

después de decorarlas

Or with al (“upon”):

al decorarlas

Both replace las paredes with las.

Why is there an article el before pasillo?

Spanish generally uses definite articles before singular, countable, specific nouns—especially rooms or parts of a building. Here el pasillo refers to a particular hallway. In English we also say “the hallway,” so both languages align in using the article.