Those who abuse the English word “nations” in our Lord’s Great Commission in service to their fervid nationalism are simply wrong. If you, dear reader, are vulnerable to being sucked into their error, here John Calvin shows the proper understanding of the Greek word ἔθνος (ethnos) commonly translated “nations.”
“Ethnos” simply means a group, race, or tribe—and in this context here in Matthew 28:19, “Gentiles.” Our Lord was not commanding His Apostles to go on crusade and take Rome. Rather, He was commanding His Apostles not to limit their proclamation of the Gospel to Jews, but now to spread it across the world making disciples of Gentiles, too. Gentiles were now included, and much of the rest of the New Testament gives a record of how angry this made Jewish racists without and within the Church.
“Ethnos” does not mean the nations of Russia, Egypt, and the United States of America. It means Gentiles.
Calvin:
"Teach all ‘nations.’ Here Christ, by removing the distinction, makes the Gentiles equal to the Jews, and admits both, indiscriminately to a participation in the covenant. Such is also the import of the term: go out; for the prophets under the law had limits assigned to them, but now, the wall of partition having been broken down, (Ephesians 2:14,) the Lord commands the ministers of the gospel to go to a distance, in order to spread the doctrine of salvation in every part of the world. For though, as we have lately suggested, the right of the first-born at the very commencement of the gospel, remained among the Jews, still the inheritance of life was common to the Gentiles. Thus was fulfilled that prediction of Isaiah, (Isaiah 49:6,) and others of a similar nature, that Christ was given for a light of the Gentiles, that he might be the salvation of God to the end of the earth.
“Mark means the same thing by “every creature”; for when peace has been proclaimed to those that are within the Church, the same message reaches those who are at a distance, and were strangers, (Ephesians 2:17.) How necessary it was that the apostles should be distinctly informed of the calling of the Gentiles, is evident from this consideration, that even after having received the command, they felt the greatest horror at approaching them, as if by doing so they polluted themselves and their doctrine.”
I will not be arguing this point. It’s very clear across the history of Bible scholarship and I simply state it here—from five centuries ago—to protect those being misled.