I've been rereading an excellent book by Peter Kreeft called Making Sense out of Suffering. There's one paragraph in particular that rang forth like a bell for me.
"All our sufferings are transformable into his work, our passion into his action. That is why he instituted prayers, says Pascal: to bestow on creatures the dignity of causality."
It seems Lewis wasn't the first to articulate how we enter into playing an active role in bringing about the will of God.
Kreeft goes on:
"We are really his body; the Church is Christ as my body is me. That is why Paul says his sufferings are making up in his own body what Christ has yet to endure in his body (Col 1:24).
"Thus God's answer to the problem of suffering not only really happened 2,000 years ago, but it is still happening in our own lives. The solution to our suffering is our suffering! All our suffering can become part of his work, the greatest work ever done, the work of salvation, of helping to win for those we love eternal joy."
That last bit of italicized text was something I had underlined years ago when I first read this book. But as you can imagine, it means much more to me now, since there is someone who I love dearly, and for whom my greatest desire is that she might find eternal joy. If I can be a part of winning that for her, I'd be the happiest man on the planet.