The Literal Commandment
"Now therefore, write this song for yourselves, and teach it to the sons of Israel; put it on their lips, so that this song may be a witness for Me against the sons of Israel. (Deuteronomy 31:19)
The literal commandment is that we should write the song of Moses (Deuteronomy 32:1-43) for ourselves.
Messiah Says
Messiah implicitly affirmed this commandment when He spoke about the Law:
"Do not think that I came to abolish the Law or the Prophets; I did not come to abolish but to fulfill. For truly I say to you, until heaven and earth pass away, not the smallest letter or stroke shall pass from the Law until all is accomplished. Whoever then annuls one of the least of these commandments, and teaches others to do the same, shall be called least in the kingdom of heaven; but whoever keeps and teaches them, he shall be called great in the kingdom of heaven. (Matthew 5:17-19)
Pictures of Messiah
The entire poem that Moses records in Deuteronomy 32:1-47 tells us about the hope and promise we have in Messiah and the great love and redemption He provides for His errant people.
In commanding us to write this poem, G-d requires us to be literate enough to read and write. He requires us to engage more than our passive ability to listen to a recitation of this poem but commands that we engage multiple senses (sight, hearing, touch) to know Who He Is.
How Messiah Fulfilled
We know that Messiah was without sin (Hebrews 4:15) so we know that He fulfilled this commandment.
Traditional Observance
This commandment is traditionally observed in a literal (but expanded!) manner: writing out an entire scroll of the Law (Genesis through Deuteronomy).
A highly regarded source of Jewish understanding regarding the commandments, Sefer HaChinuch, offers this insight:
Whoever does not find it possible to write it [the scroll] with his own hand should hire someone that should write it for him. About this it is written, Now therefore write for yourselves this song, and teach it to the Israelites (Deuteronomy 31:19); in other words, write for yourselves the Torah, in which there is this song.
At the root of the precept lies the reason that it is known about human beings that they carry out all their matters according to the preparation [of resources] that is available to them. Therefore He (blessed is He) commanded us that every single Jew should have a Torah scroll ready about him [at hand], so that he can read it always, and he will not need to go for it to the home of his friends, in order that he may learn to fear the Lord (Deuteronomy 17:19), and thus he will know and come to understand His mitzvoth [commandments], that are more precious and cherishable than gold, even much fine gold.
Other Notes
While the commandment itself seems clear, the latter part of the verse is often overlooked:
...that this song may be a witness for Me against the sons of Israel.
This song (and its numerous copies) is to stand as witnesses against the sons of Israel indicating that G-d knew of their sin and rebellion long before it ever occurred. It also reflects His intention to perform the work required to redeem them and restore them as His own cherished people.
We are able to fulfill this commandment today and should write out the song of Moses for ourselves.
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