What "LAW" is John referring to?

"The beloved disciple, who listened to the words of Jesus on the

mount, writing long afterward under the inspiration of the Holy Spirit, speaks of the law as of perpetual obligation. He says that "sin is the transgression of the law" and that "whosoever committeth sin transgresseth also the law." 1 John 3:4. He makes it plain that the law to which he refers is "an old commandment which ye had from the beginning." 1 John 2:7. He is speaking of the law that existed at the creation and was reiterated upon Mount Sinai."
Thoughts From The Mount Of Blessing p.48 E.G.W.