When I was a child in Catholic school, the nuns made much of praying for "the holy souls in purgatory." On this, their feastday, it was a ritual duty whose premises seemed terribly abstract even to me, young master of the catechism. We were being enjoined to do something for dead half-people we could not see; and even taking on faith that our prayers did them some good, we couldn't see that either. Indeed, it wasn't until I reached college age that I could see the point of purgatory at all. Now I don't know what I'd do without the hope of it. I'm rather dubious about my chances of making it straight to heaven, unless I die heroically as a martyr or saving lives— which of course would be too gratifying, which is why it probably won't happen. It's a lot harder to live for Christ, which we all must do, than to die for him, which relatively few are granted the privilege of doing.
Non-Catholics who think it important to be catholic—chiefly, the Orthodox and the Anglo-Catholics—object not so much to the idea of purgatory as to the fact that Rome has defined it as dogma (cf CCC 1031). In that respect it is like several other Catholic dogmas, not least of which is the dogma that the pope can define dogma unilaterally and infallibly. Protestants tend to shy away from it as unbiblical (which it isn't) and as an excuse for corruptions that Luther rightly castigated in the late-medieval Catholic Church (which indeed it once was). But I am more and more convinced that it's just—well, if not obvious, then at least quite congruent with Christian experience. In 1769 James Boswell had this exchange with Samuel Johnson:
Indeed. Even if it does not occupy one's daily thoughts, purgatory reminds us that many of us halfway-decent folk die without having completed the spiritual growth for which we are meant. If one believes in an afterlife at all, the only real alternative to purgatory is reincarnation, which seems to me philosophically untenable inasmuch as it assumes that the soul is the person, not just the most important part of the person. Even so, the element of truth in the Hindu and Buddhist doctrine of reincarnation is the same as that in purgatory: we do not attain complete bliss until we have been purified for it. Obversely, I find it comforting to be assured by the authority of the Church that I can enter the next life definitively saved without yet being fit for the company of heaven. I also find it comforting to know that the dying to self I should be doing as part of living for Christ will be consummated later if it isn't sooner. But for that reason I don't think I'll be comfortable in purgatory. I'd want to be prayed out of it. And so I offer my prayers accordingly for those already there.