Like many languages (but unlike Greek or Hebrew or English), Spanish uses a formal vs. informal second-person pronoun (a familiar vs. a respectful “you”). Spanish Bibles all use only the informal second-person pronoun (tú), with the exception of Dios Habla Hoy (third edition: 1996) which also uses the formal pronoun (usted). In the referenced verses, the formal form is used.
Many languages distinguish between inclusive and exclusive first-person plural pronouns (“we”). (Click or tap here to see more details)
The inclusive “we” specifically includes the addressee (“you and I and possibly others”), while the exclusive “we” specifically excludes the addressee (“he/she/they and I, but not you”). This grammatical distinction is called “clusivity.” While Semitic languages such as Hebrew or most Indo-European languages such as Greek or English do not make that distinction, translators of languages with that distinction have to make a choice every time they encounter “we” or a form thereof (in English: “we,” “our,” or “us”).
For this verse, translators typically select the exclusive form (excluding the readers of the letter).
Source: Velma Pickett and Florence Cowan in Notes on Translation January 1962, p. 1ff.
Note that many Common Language translations (the GermanGute Nachricht Bibel, the DutchBijbel in Gewone Taal, the EnglishGood News Translation, the FrenchBible en français courant, the Brazilian PortugueseNova Tradução na Linguagem de Hoje, the IndonesianAlkitab dalam Bahasa Indonesia Masa Kini, or the SpanishDios habla hoy) use the singular first personal pronoun (“I”) rather than the plural form (“we”). (Source: Paul Ellingworth in The Bible Translator 2005. p. 226ff. )