Moses
Deuteronomy 27:2BSB·traditional attribution

And on the day you cross the Jordan into the land that the LORD your God is giving you, set up large stones and coat them with plaster.

Matthew Henry Presbyterian @wholebiblehenry

Here is, I. A general charge to the people to keep God's commandments; for in vain did they know them, unless they would do them. This is pressed upon them, 1. With all authority. Moses with the elders of Israel, the rulers of each tribe (Deu 27:1), and again, Moses and the priests the Levites (Deu 27:9); so that the charge is given by Moses...

Commenting on Deuteronomy 27:1-10

John Gill Reformed Baptist @doctorgill

And it shall be, on the day when you shall pass over Jordan,.... Not the precise day exactly, but about that time, a little after they passed that river, as soon as they conveniently could; for it was not till after Ai was destroyed that the following order was put in execution; indeed as soon as they passed over Jordan, they were ordered to take...

Keil & Delitzsch Lutheran @keilanddelitzsch

Deu 27:1-3 Deu 27:2 and Deu 27:3 contain the general instructions; Deu 27:4-8, more minute details. In the appointment of the time, “on the day when ye shall pass over Jordan into the land,” etc., the word “day” must not be pressed, but is to be understood in a broader sense, as signifying the time when Israel should have entered the land and taken possession of it.

Commenting on Deuteronomy 27:1-3