The Literal Commandment
Whatever I command you, you shall be careful to do; you shall not add to nor take away from it. (Deuteronomy 12:32)
This tells us that we should not change the number of commandments (neither add nor take away) but it also says we should not change the scope of any commandment. For example, while we are commanded to bind tefillin upon the head, we should not bind two tefillin upon the head because that would be expanding the scope of the commandment.
Messiah Says
Messiah affirms the commandment to "not add any commandments to the Law" implicitly:
"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)
If we "add any commandments to the Law", we are annulling G-d's Law and replacing it with our own.
Pictures of Messiah
How does this commandment picture Messiah? To add to the commandments is to add to G-d's revelation of Himself and declare that somehow Scripture is inadequate or incomplete. Scripture, itself, declares that is not true:
The law of the LORD is perfect, restoring the soul; The testimony of the LORD is sure, making wise the simple. (Psalm 19:7)
Messiah is the Torah made flesh (John 1:14) and this commandment reveals that we need not add anything to Him. Messiah's faithful life of obedience, upholding the commandments, is perfect and His grace is sufficient.
How Messiah Fulfilled
Messiah obeyed the commandment to "not add any commandments to the Law" by not adding any commandments to the Law. Instead of adding or extending any of them, He instead gave them to us in their intended fullness.
Do not think that I came to abolish the Law or the Prophets; I did not come to abolish but to fulfill. (Matthew 5:17)
Traditional Observance
The traditional observance of this commandment is expressed by both not adding any commandment (increasing the number) as well as not expanding any commandment (increasing its scope or significance).
The Sefer haChinnuch says that this command only applies to positive precepts of the Torah. Violation only occurs if one performs a commandment and intends to do so outside of its intended scope/time:
Thus too if someone sits in a sukkah (booth) after the festival, with the intention to fulfill the precept of sukkah, although he knows that the proper time for it has gone. For there is no transgression on account of the injunction, you shall not add, unless there is an intention to fulfill a precept. So too if someone took up a lulav after the festival [of Sukkoth] intending to fulfill the precept with it, despite his knowing that the festival was over.1 [Emphasis added]
Other Notes
We are able to fulfill this commandment today and should not add to the commandments from the Law nor expand their scope.
Why? First, because G-d has so commanded it. Second, because Messiah, Himself, did not add to them. Third, because doing so would suggest that G-d's Word is insufficient and requires us to add to it: somehow G-d needs our help. Our job is to both obey (i.e. perform as possible) and keep (uphold as true and good) the commandments:
Let your light shine before men in such a way that they may see your good works, and glorify your Father who is in heaven. (Matthew 5:16)
<><
