“You shall not go with them, neither shall you curse the people.” He does not hint at anything with regard to the people, for they all lay before his view, but [he refers] to the mystery of Christ pointed out beforehand. For as He was to be born of the fathers according to the flesh, the Spirit gives instructions to the man (Balaam) beforehand, lest, going forth in ignorance, he might pronounce a curse upon the people. Not, indeed, that [his curse] could take any effect contrary to the will of God; but [this was done] as an exhibition of the providence of God which He exercised towards them on account of their forefathers.
Source: Fragments from the Lost Writings of Irenaeus (New Advent)