A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
deu 27:2THE PEOPLE ARE TO WRITE THE LAW UPON STONES. (Deu 27:1-10)
it shall be on the day when ye shall pass over Jordan--"Day" is often put for "time"; and it was not till some days after the passage that the following instructions were acted upon.
thou shalt set thee up great stones, and plaister them with plaister--These stones were to be taken in their natural state, unhewn, and unpolished--the occasion on which they were used not admitting of long or elaborate preparation; and they were to be daubed over with paint or whitewash, to render them more conspicuous. Stones and even rocks are seen in Egypt and the peninsula of Sinai, containing inscriptions made three thousand years ago, in paint or plaister. By some similar method those stones may have been inscribed, and it is most probable that Moses learned the art from the Egyptians.
deu 27:3thou shalt write upon them all the words of this law--It might be, as some think, the Decalogue; but a greater probability is that it was "the blessings and curses," which comprised in fact an epitome of the law (Jos 8:34).
deu 27:5there shalt thou build an altar . . . of whole stones--The stones were to be in their natural state, as if a chisel would communicate pollution to them. The stony pile was to be so large as to contain all the conditions of the covenant, so elevated as to be visible to the whole congregation of Israel; and the religious ceremonial performed on the occasion was to consist: first, of the elementary worship needed for sinful men; and secondly, of the peace offerings, or lively, social feasts, that were suited to the happy people whose God was the Lord. There were thus, the law which condemned, and the typical expiation--the two great principles of revealed religion.
deu 27:11THE TRIBES DIVIDED ON GERIZIM AND EBAL. (Deu 27:11-13)
These shall stand upon mount Gerizim to bless the people . . . these shall stand upon mount Ebal to curse--Those long, rocky ridges lay in the province of Samaria, and the peaks referred to were near Shechem (Nablous), rising in steep precipices to the height of about eight hundred feet and separated by a green, well-watered valley of about five hundred yards wide. The people of Israel were here divided into two parts. On mount Gerizim (now Jebel-et-Tur) were stationed the descendants of Rachel and Leah, the two principal wives of Jacob, and to them was assigned the most pleasant and honorable office of pronouncing the benedictions; while on the twin hill of Ebal (now Imad-el-Deen) were placed the posterity of the two secondary wives, Zilpah and Bilhah, with those of Reuben, who had lost the primogeniture, and Zebulun, Leah's youngest son; to them was committed the necessary but painful duty of pronouncing the maledictions (see on Jdg 9:7). The ceremony might have taken place on the lower spurs of the mountains, where they approach more closely to each other; and the course observed was as follows: Amid the silent expectations of the solemn assembly, the priests standing round the ark in the valley below, said aloud, looking to Gerizim, "Blessed is the man that maketh not any graven image," when the people ranged on that hill responded in full simultaneous shouts of "Amen"; then turning round to Ebal, they cried, "Cursed is the man that maketh any graven image"; to which those that covered the ridge answered, "Amen." The same course at every pause was followed with all the blessings and curses (see on Jos 8:33-34). These curses attendant on disobedience to the divine will, which had been revealed as a law from heaven, be it observed, are given in the form of a declaration, not a wish, as the words should be rendered, "Cursed is he," and not, "Cursed be he."