Matthew 18:7 reads:
Woe to the world because of offenses! For offenses must come, but woe to that man by whom the offense comes!
I'm not anti-Semitic and I don't subscribe to the idea that Jews are cursed, but let's not overstate our case.
Then omniscience and grace mean nothing. God knew what was coming long before it happened just like he knew each of us before we were born. He used the Jews and Romans to execute His plan.
Well yes, because he sins and all sin results in woe. That might be a specific hint about the rebel disciple, Judas, who preferred to kill himself rather than begging God for forgiveness (which if it had hypothetically happened would have been granted).