I used to see nationalism as inherently a sin. Now I would say it easily becomes a sin while not necessarily so in and of itself. It is hard to find a good balance sometimes on subjects, and of course we want to think in terms of what scripture teaches with due consderation of the church’s teaching and practice through the centuries.
The church state relationship which began with the Roman emperor Constantine whose conversion to Christianity resulted in “the Holy Roman Empire.” Rome actually becoming a Christian state, ends up being questionable at best. While the state afforded the church protection, it really offered much more with strings attached. You had to be baptized as a citizen; it was after all a Christian nation by law. Yes, the gospel figured in but when such is coerced on families by the state, we begin to wonder where the scriptural precedent is for that unless one turns to the Old Testament. It doesn’t seem warranted from a reading of the New Testament and what we see in regard to the state in those books.
Paul used his Roman citizenship to help him preach the gospel especially to the Gentiles, which was his calling. And he could preach it to the Jews as well, since living under the authority of a state other than Israel was nothing new; we’re easily reminded of Daniel in the Old Testament along with others.
We can love our country and hope and pray the best for it. But we must beware that the church not be coopted into the goal of the state. Some Christians today want to “bring America back to God” and consider the United States at its founding, a Christian nation. That might be considered the case only in a cultural sense. I don’t agree with it, believing that the nation was built on a Modernist Enlightenment foundation, the scriptures read from that. And certainly the sin of slavery along with subjugation of native peoples is no small problems in contending for such.
What we don’t want is a civil religion which some Christians seem to want to promote, a Christianity which promotes guns and glory and even brings in the cross to sanction that. We need to think twice and more before we buy into that. We are to pray for those in civil authority (1 Timothy 2). The church is to receive protection from the state with no strings attached except submission in terms of laws which do not contradict God’s will, but hopefully promote a just peace (Romans 13). But in this life that won’t always be the case as we know all too well by considering the twentieth century alone right up to the present day.
The nature of the church sets it apart in its allegiance to the gospel and King Jesus, the good news of Jesus. We are not to be bearers of the sword, but of the cross. We are to live and die for Jesus and the gospel no less. Even while we honor those who put their lives on the line in the work of the state. But the church must beware lest its witness be compromised, sullied and possibly even lost in allegiance to the state. To a bad state, or even to one that is seeking to function well. Nationalism as in love of one’s nation is one thing, but to do so as those committed to the state’s agenda in full can easily be another. Nationalism can indeed become a sin.