If you are studying Spanish, you know we use something called the personal A whenever a person is the object of the action. If you have already forgotten about this, allow me to quickly revisit it with you.
What's a personal A again?
In phrases like these:
Luis loves his wife.
She respects her boss.
We all hate the president.
We have a subject: Luis, she, we all, a verb: loves, respects, hate, and an object: his wife, her boss, the president. All the objects happen to be people, which means they need a personal A in Spanish:
Luis ama a su esposa.
Ella respeta a su jefe.
Todos nosotros odiamos al presidente.
So, why do we need it?
The basic answer that all teachers give students at the beginning of their Spanish journey is that it is a distinction we offer to people to differentiate them from things. Well... This can be an initial explanation, but, come on! We all know the difference between "his wife" and "his car" (even though some men treat their cars like they treat their wives sometimes :P)
The real reason is that in Spanish, the word order is not as strict as it is in English. The latter follows a fairly unmovable and logical sentence structure. For example, you all know that the adverb "already" is always used before the verb:
I already ate.
While in Spanish, we couldn't care less about the placement of that word in the sentence:
Yo ya comí. // Ya yo comí. // Yo comí ya.
They're all the same for us.
Well, something similar happens with the objects of our sentences, their place in the sentence is not set in stone. That way, the sentence Carlos loves his wife translates into Spanish as:
Carlos ama a su esposa.
But here are other equally valid, though less frequent, options in conversations:
Carlos loves his wife:
Carlos ama a su esposa. (Most common in conversation)
Carlos a su esposa la ama.
Ama a su esposa Carlos.
A su esposa la ama Carlos.
In all the previous cases, the sentence has not changed in meaning and the possibility of confusion is nonexistent because we all know that the person with the personal A is not performing the action but receiving it. If we removed the A, the sentence would be confusing or completely change from Carlos loves his wife to his wife loves Carlos. It's important to know that the three previous sentences are not common in daily conversation [although not impossible], but they are possible in literary texts, formal, and poetic language.
Another example:
She gave Anna a present
Ella le dio un regalo a Ana.
A Ana ella le dio un regalo.
Ella a Ana le dio un regalo.
Ella a Ana un regalo le dio.
A Ana un regalo le dio ella.
This also explains why we do not use the personal A with objects since we know that inanimate objects are incapable of doing anything, so changing the order of the sentence won't be confusing.
Now, since examples are the best way to understand things, let me show you a couple of extracts from books to see how this piece of information we just learned is crucial to understand them.
The following dialogue between a mother and a son is taken from the short story "Algo grave va a ocurrir en este pueblo" (Something serious is going to happen on this town) by Gabriel García Márquez*:
* Hyphens are used in Spanish to indicate someone is talking.
— Hombre, porque no pudo hacer una carambola sencillísima estorbado con la idea de que su mamá amaneció hoy con la idea de que algo muy grave va a suceder en este pueblo.
Entonces le dice su madre:
— No te burles de los presentimientos de los viejos porque a veces salen.
Entonces le dice su madre, at first glance, it seems to be saying "so he says to his mother," but it doesn't, instead it says "so his mother tells him"; how do we know? Because "su madre" does not have a personal A, therefore, she is the subject of the verb decir, she is performing the action.
Let's see another example taken from the book El Principito (The Little Prince) where the main character, the little Prince, is having a conversation with a flower. Since the flower in this story is a character with a personality, we're going to have the same grammar we use with people:
—Adiós —le dijo a la flor. (He said to the flower)
—He sido una tona —le dijo al fin la flor. (The flower finally said to him)
And here's another example, look at how the inclusion of the personal A changes the answer to each question.
– Laura estaba visitando a sus padres. (Laura was visiting her parents)
– ¿A quién estaba visitando? (Who was she visiting? Asking who receives the action)
– A sus padres. (Her parents)
– ¿Quién? (Who? Asking who does the action)
– Laura.
See? The personal A not only makes sense but is also very necessary for understanding a conversation or a text. So, please, try not to forget it.