In this parashah we read about the last mitzvah of the Torah. It is the mitzvah of writing a Torah book (Sefer Torah).
God commands every Jew to write a book for himself. However, most of us are not scribes, so God allows us to hire someone else to write it for us.
The work of a scribe is very expensive. It takes a lot of time and effort to write a Sefer Torah. Not everyone can afford such work.
Therefore, HaShem gave us another way to fulfill this commandment. Many people can share in the writing of a Sefer Torah by purchasing a letter. In this way, fulfilling the mitzvah of writing a Sefer Torah unites us all with Ahavat Israel – amor al prójimo.
Di-s nos manda a escribir un Sefer Torá con el versículo «Escriban esta canción [La Torá] para ustedes». HaShem llama a la Torá una canción, enseñándonos que debemos observar sus mandamientos con alegría y regocijo.
Adapted from Please tell me what the Rebbe says.