"Many even of the authorities believed in him, but for fear of the Pharisees they did not confess it. . . . for they loved the glory that comes from man more than the glory that comes from God" (John 12:42,43).
My experience is that the modern church has put the accent on the believing half, not so much on the confessing half. But as I read the above verses together with Romans 10:9 (unless I am bent on watering it down), I see a double confirmation that salvation itself requires both internal and external manifestations: "If you confess with your mouth that Jesus is Lord and believe in your heart that God has raised him from the dead, you will be saved."
So were the people in John 12:42 saved, with that kind of non-confessing faith? And are people in our day who "believe in him" saved, if we never get around to "confess with our mouth" in daily interactions? It's a terrifying thought.
I will tell you that for most of my "Christian" life I "believed in him" (that was my voter registration card status, as it were), but did not confess him. That is to say, if you had a tape recording of my complete utterances from 1975 to about 2005, you would hear complaining, defeatism, and all manner of worldly talk. I am grateful that I did not die in those years.
Nor do I think we wiggle out of this hard biblical proposition by "counting" as "confessing Christ" those formal occasions such as Church membership Sundays, or reciting the Lord's Prayer or Apostles' Creed in worship services. What God has in mind is a lifestyle that confesses him like breathing-daily conversations that acknowledge him, and drop his Name as naturally as we talk about the weather or our auto mechanic.