Our culture thinks rank skepticism (or even spiritual nihilism) is humility, and hipster Christians have overcontextualized themselves to the point where they seem to think that's true. Strong convictions—the very thing Paul calls for here—are out. If you don't undergo some kind of major paradigm shift in your theology and your worldview every few years or so, you are not only hopelessly behind the times, you are incurably arrogant, too.
That's why, according to any postmodern way of thinking, dogmatism is to be avoided at all costs, diversity is to be cultivated no matter what, and tolerance means never having to say "You're wrong."
That's not "humility"; that's unbelief.
It's not arrogant to have firm, immovable biblical convictions. In fact, it is our duty to be precise and thorough in our doctrine, and to come to strong, mature, biblically-informed convictions. Paul even named this as one of the necessary evidences of authentic faith: "If indeed you continue in the faith, stable and steadfast, not shifting from the hope of the gospel that you heard" (Colossians 1:23). We are not to be "children, tossed to and fro by the waves and carried about by every wind of doctrine" (Ephesians 4:14). Stability is a good and precious virtue—a necessary virtue for church leaders especially. Peter wrote, "Take care that you are not carried away with the error of lawless people and lose your own stability" (2 Peter 3:17).
Watch out for those who undergo regular, major paradigm shifts in their thinking or revamp their whole theology every few years—avoid them. Double-minded men are unstable in all their ways.
Yeah, but isn't it wrong to be obstinate and inflexible?
Well, it certainly can be, but do you know what the Bible identifies as the very worst kind of stubbornness? It's the obstinacy of refusing to be steadfast in our conviction that the Word of the Lord is true. Scripture condemns such people as "a stubborn and rebellious generation, a generation whose heart was not steadfast" (Psalm 78:8). How were they "stubborn" without being steadfast? "Their heart was not steadfast toward him; they were not faithful to his covenant" (v. 37). That's the very height of arrogance.
"Stand firm." That's a command. "Stand firm in the faith." The definite article is significant. There is only one true faith, and if your faith in Scripture isn't strong enough to affirm even that fact without equivocation, you really need to ponder very carefully what Paul is saying here. Because in all likelihood, that question will be put to you by an unbeliever ("Is conscious faith in Jesus really the only way to heaven?"), and you need to be ready to give an answer. I'm amazed and appalled at the parade of evangelical celebrities who have flubbed that question on Larry King Live or other national platforms.
"Stand firm in the faith," Paul says, and if you are tempted to tone that down, apologize for it, or explain it away because it conflicts so dramatically with the spirit of this age, then you need to repent of that attitude and ask God to give you more conviction and more courage.