Parshat Vayelech includes the commandment for every Jew to write a song for themselves (31:19), which Rashi says is referring the following Parsha, Haazinu. The sages derive from this rule the final of the 613 commandments that each Jew has to take part in the writing of a Torah scroll. Why would we be required to write our own song, and then be given the song to sing? Also, how is the requirement to write our own song the same as the requirement to take part in scribing our own Torah?
If we apply the concept of this weekly Dvar Torah, we can easily understand the Torah’s final commandment: If we take any commandment in the Torah and personalize it, although its source is the Torah, its ownership is very personal. Songs, too, sound different when sung by different people. In fact, music becomes even more personal because it’s a more emotional medium. That’s exactly why the Torah chose music as the metaphor to teach us about personalizing the Torah to make it special for ourselves. The Torah wants us to internalize it so much that we sing about it. If we accomplish this, we’ve fulfilled the final commandment of writing our own Torah – with all the harmonies that accompany it.