I grew up Baptist, so, following Baptist custom, I was not baptized as an infant. Rather, I was baptized when I was 6, after I had made a commitment of my own to Christ. I was young, but old enough to make a genuine commitment, one that I have not turned away from.
When I decided in my 20s to become Episcopalian, there was a requirement that I be confirmed. That made me uncomfortable, because it seemed as though it was invalidating my baptism. In the Baptist tradition, baptism serves as a public profession of faith, and confirmation seemed to be saying that my prior commitment to Christ wasn't good enough.
However, I found another way to look at it. During my college years, I came to the realization that the existence of God (probably) cannot be proved, that there is no certainty anywhere in the religious realm -- no inerrant Scripture, no infallible pope, no infallible councils, no complete set of proofs of Christianity's basics, none of it. Very disturbing to a mathematician like myself who craves certainty. So, on the far side of all that, I had to make a decision: Am I going to continue to follow Christianity anyway, despite all of this uncertainty? And I decided, yes. That decision came approximately at the time when I was being asked to go through confirmation, so that's what confirmation came to mean to me: the decision to continue to follow Christ, even though I cannot know whether I am correct. As Lewis put it, I will act as a Narnian even if there is no Narnia.
That can't be what the ancient church had in mind when they designed confirmation, so many centuries before the Enlightenment, but there it is.
Confirmation also, of course, marked my formal acceptance into the Episcopal Church, on the last Sunday in Epiphany, 1985, and each year on that day I remember with gratitude the church community who welcomed me all those years ago.