Questions & Answers about Él trabaja para ti y es incansable.
Why do we use para instead of por in this sentence?
We use para here because it indicates employment or the recipient of the work. This means you are his boss or the one employing him. If the sentence said trabaja por ti, it would change the meaning to say he is working on your behalf (perhaps covering your shift because you are sick) or that you are his motivation.
Why is it para ti and not para tú or para te?
After prepositions like para, de, or a, you must use a prepositional object pronoun. For the informal 'you', that pronoun is ti. The pronoun tú is only used when 'you' is the subject of the sentence, and te is used as a direct or indirect object attached to verbs.