Mat 5:34
But I tell you, do not swear an oath at all
Who is persecuting you?
Nobody persecutes me, I'm armed to the teeth and I don't yield. Christianity as a whole is under persecution in some form or another.
Matthew pretty much also said to obey every aspect of Jewish law, even that which was fulfilled by the Crucifixion. The word "swear" is used in both Old and New Testaments in at least 60+ verses, 7 times in Matthew alone. Matthew and James are the only ones to state it as something negative. Paul didn't think it was negative, and he was the only other one to use the term in the NT.