Charles Ellicott Commentary Matthew 10:18

"yea and before governors and kings shall ye be brought for my sake, for a testimony to them and to the Gentiles." — Matthew 10:18 (ASV)

You shall be brought before governors and kings — The words are significant as looking forward (if we assume the unity of the discourse) to that future work among the Gentiles which the Twelve were told they were not yet to enter. “Rulers” always stands in the New Testament for the governors (proconsuls, procurators, and others) of the Roman Empire. “Kings” at least includes, even if it does not primarily indicate, the emperors themselves.

Against them — Rather, unto them. The word is simply the dative of the person to whom we address our testimony, not necessarily involving any hostile or even reproving purpose.