Acts 10:35 But in every nation whoever fears Him and works righteousness is accepted by Him.
I think it must have been hard for the disciples to accept how Jesus wanted them to go out into all the world to preach the gospel; they were a protective race, a God-fearing race.
In their history they learned how God had wiped out other nations and how God did not want them to mix with others, and yet God was saying they needed to mix now.
God was not going against His word; rather He was opening new doors for them to preach, not to ignore His laws in.
When God sends you out to spread the gospel, He does not send you out to go and act like the local people.