In Deuteronomy 27-28, God told Israel to build a monument on Mt. Ebal and carve on it the words of the Law. Then he told half of them to stand there and pronounce curses for disobedience. The other half were to stand on Mt. Gerizim and pronounce blessings for obedience.
An antinomian might say that the Law was written on Ebal because the Law brings a curse. Superficially that sounds good to someone who has avoided studying Torah, but it falls apart when one remembers that the curses are only for disobedience. The blessings that the other half of Israel pronounced from Gerizim are also included in the Law. It is true that the Law brings a curse, but the Law also brings a blessing.
God’s Law was not present only on Mt. Ebal. It was there on both mountain tops, but where was it on Mt. Gerizim?
Here’s a hint: It wasn’t carved on stone.
God wrote his Law on stone at Sinai because the hearts of Israel were too hard to accept it, but that’s not where he wants it to remain. He has promised that in the New Covenant, his Law will be written on flesh. (See Jeremiah 31.) To those for whom the Law remains only on stone, whose hearts are too hard to receive it, it is most certainly a curse, but to those who internalize it, who invite God to write it on their hearts, who learn to love it, to them the Law is full of blessings.
This is why God told Israel to write the Law on a stone monument on Mt. Ebal: hard hearts and the Law on stone on one hand and the Law written on hearts of flesh on the other.
Update 08/30/2010: In a podcast recorded last year, Grant Luton of Beth Tikkun Messianic Fellowship explained why the altar was built on Mt. Ebal. Yeshua did not come for the hale, but for the sick, for those still under the authority of the Law.