How does it NOT teach that?
Seriously. I've never been nuts for the "treasury of merit" image. But I AM nuts for the life of Christ living in the redeemed so that they say, with Paul, now I live, yet not I but Christ lives in me.
And what Christ does on earth is suffer and die a lot. And the benefits of His atoning suffering and death are applied as He, the Head of the body, the Church. wills
As we participate in his life, as we put off the old man, as the flesh dies and we put on Christ with whom our life is hid, we, in our view, put on an incredibly undeserved intimate union with Him, so that we may share in his work, and in His love, soaked in the torrent.
Of course, to the extent that I consider this MY work in any proprietary way, that is old man, that is flesh, that is death and rags. There is no room for pride, only for astonished gratitude.
Now as to the other half, The Church "applying," well, I don't expect to close the sale, but you know what we think apostle means, and the rest follows from that.
Darn, this is so inadequate. It'll serve as a token, a marker, maybe.
Just previous, Paul writes, “21 And you, who once were alienated and hostile in mind, doing evil deeds, 22he has now reconciled in his body of flesh by his death, in order to present you holy and blameless and above reproach before him”
Reconciliation came (now reconciled, past tense) “by his death”...not by any suffering of the church now. And his goal is “to present [us] holy and blameless and above reproach before him”.
But there is a lot of suffering that goes on, both to bring us to the image of Christ, which our flesh fights tooth and nail & painfully, and to bring the gospel to all who need to hear it - a part of the work of redemption.
So Paul is not saying his suffering buys anyone redemption or salvation, but that he is participating as one with Christ in bringing all the gospel and being conformed to Christ.
As you put it, and I’m certain Paul would strongly agree, “But I AM nuts for the life of Christ living in the redeemed so that they say, with Paul, now I live, yet not I but Christ lives in me.”
As Paul goes on to say, “For this I toil, struggling with all his energy that he powerfully works within me.”
The death of Christ was sufficient for the forgiveness of all our sins. But salvation also refers to our sanctification (calling out from a sinful world), and that involves pain from us and others. And the proclaiming of the gospel likewise, as you point out, “And what Christ does on earth is suffer and die a lot.”
So we agree on a lot, and disagree on some. But our justification is past tense, while our sanctification is ongoing.