Parashat Vayeilekh: Halakhah

Halakhah הֲלָכָה

The 613th mitzvah in the Torah is the commandment for each and every person to write a סֵפֶר תּוֹרָה (sefer Torah, Torah scroll). How cool is that!
Hazal base this mitzvah on a pasuk near the end of Vayeilekh:
וְעַתָּ֗ה כִּתְב֤וּ לָכֶם֙ אֶת־הַשִּׁירָ֣ה הַזֹּ֔את וְלַמְּדָ֥הּ אֶת־בְּנֵֽי־יִשְׂרָאֵ֖ל שִׂימָ֣הּ בְּפִיהֶ֑ם...
Now, write down this shira (song/poem) and teach it to Benei Yisrael—put it in their mouths
Even one letter
Rav says that writing a Sefer Torah is so important that if you do it, it’s as if you received the Torah on Har Sinai. Rav Sheshet adds that even if you write a single letter in a Torah scroll, it’s considered as if you wrote the entire thing (Talmud Bavli Menahot 30a).
Because of Rav Sheshet’s teaching, it’s a common practice that when a community orders a new Sefer Torah to be written, we try to give everybody in the community a chance to write a letter (with the help of a trained סוֹפֵר (sofer, scribe)).
Parchment scroll vs. books
According to the Rambam, the only way to observe the mitzvah of writing a Sefer Torah is to actually write the words of the Torah on parchment with ink (Hilkhot Tefillin, Mezuzah u-Sefer Torah 7:1) .
But the Rosh has a different perspective. He says the purpose of this mitzvah is to be sure that everyone can study Torah. So he says we can fulfill this mitzvah by having a library of Jewish books in our homes. (Hilkhot Sefer Torah 1)
R. Yosef Karo agrees with the Rosh, that today owning Jewish books is a way to observe this mitzvah. But he also says that if you find an opportunity to participate in actually writing a sefer Torah, it’s certainly a mitzvah to do so! (Bet Yosef Yoreh Deah 270)