From Chabad.org: Balak takes Bilaam to another location, hoping that this new venue would be more inauspicious for the Jews. They again build altars and offer sacrifices, and again G‑d dictates blessing for the Jews which Bilaam repeats. “G‑d does not look at evil in Jacob, and has seen no perversity in Israel; the L-rd, his G‑d, is with [Israel], and he has the King’s friendship…”
After Balak takes him to a different location, one where there might be weakness (he took him to the spot where Moshe would eventually die), Bilaam explains that he has no choice but to say what G-d tells him to say, and G-d instructed him to bless the Jews again. He then goes on to bless the Jews by saying that G-d does not see evil in Jacob, nor perversity in the Jews. How is this a blessing? It sounds more like a fact. But the blessing is that although we know evil and perversity does exist, G-d overlooks it long enough for us to correct our mistakes, demonstrating His love and friendship (Passuk 21: Rashi).