Thanks for asking about this. The idea of “offering things up” is actually pretty central to my understanding of Christianity, and I’m happy for an opportunity to talk about it.
I don’t remember where I first heard of the idea, but I think it has its basis in one of St. Paul’s letters — let me look it up — it’s Colossians 1:24.
I rejoice in what I am suffering for you, and I make up in my flesh what is lacking in Christ’s afflictions, for the sake of his body, which is the church.
The verse is a mysterious for several reasons, the most obvious one being that it seems to say that Christ’s sufferings were insufficient somehow, since there was something “lacking” in them. I don’t believe that is what St. Paul is saying, but I’ll come back to that afterwards.
The main idea here, as I understand it, is that when we suffer, if we accept that suffering the same way Christ did — as something which is the will of the Father in some way, or at least as something which the Father has allowed us to undergo — then, by that act of acceptance, we transform the suffering (or allow it to be transformed) from an evil into a positive good.
The principle that is active here is the same as the principle behind the Crucifixion itself: that suffering, when it is accepted willingly — and not with a spirit of avoidance or even merely a spirit of resignation — has a kind of salvific power. (I’m not sure whether it is suffering per se that has that salvific power, or only suffering in a particular context; more on this later.) So just as Christ’s crucifixion brought about good for all, so our mini-crucifixions can bring about good for those for whom we decide to undergo them.
When I say “mini-crucifixions”, I mean any suffering that we undergo, whether it is big or small. And I think that, since the suffering in question is our own suffering, then we have the right or the power to decide who will benefit by this suffering. (I don’t know whether this particular aspect of my belief is theologically kosher, but I believe it nevertheless, and I don’t see anything wrong with believing it. Your mileage may vary.)
So, to give you an example, if I’ve got a headache, I can either complain about that headache; or I can be resigned and wait until it goes away; or I can make a positive act of the will to accept that headache, or even to choose it. I can say, “I accept this headache, Father, and please use it for [x], who is depressed right now.” Or if I hate getting out of bed right when the alarm rings, which I do, I can say “I accept this lack of snoozing, Father, and please use it for [x], who is struggling with addiction.”
The suffering doesn’t have to be related to the thing you’re offering it up for — if suffering is a kind of spiritual currency, then I believe it is fungible.
Back to the verse from Colossians, I think we can see why, in some sense, Christ’s suffering is only complete when we participate in it. It makes sense if we remember that we, as the Church, are in fact Christ’s body — not only in a metaphorical sense, but in a very real (albeit mysterious) sense; this is (at least part of) what the Church means when she talks about “the mystical body of Christ”. So when we suffer, it is Christ who is suffering in us; and when he suffered on Calvary, he brought all of our suffering with him, as though it were his own; and that this is especially true of that suffering which we consciously decide to bring to him, and to unite to him.
And this, I guess, is why our suffering has any merit at all — not that suffering per se has this power (I’m not sure about that), not just because (as I glibly said above) suffering is “spiritual currency”, but because it is His suffering; and it becomes his suffering precisely to the extent that we decide to unite it to him, by accepting it in the same way that he did.
By the way — although this point could really be a whole nother email in itself — all of this is deeply related to the Mass. The Mass, as you know, is a re-presentation of Christ’s sacrifice on Calvary; not that the sacrifice happens again, but that it is somehow made present again, or we are made present to it, as though every Mass opened a wormhole in space and time with its other end at Calvary.
So the Mass is the moment where it all comes together: we bring our little crucifixions to the very site of the big Crucifixion — and, by the way, I think this is what we really ought to be doing during the offertory: calling to mind all of the things that we want to bring to Jesus, the good things and the bad things (because you can offer up joys as well as sufferings!), everything we want to offer to him. So we bring our little crucifixions to Christ’s big Crucifixion, and he takes them up and offers them to the Father along with his own joys and sufferings; and from there they explode outward, spreading their saving power over the whole world.
He takes our little loaves and fish and multiplies them, and he uses them to feed everyone else, and to feed us too!, and what he feeds us on is his own body and blood — which is also our own body and blood — which is becoming more His as we are transformed more and more into Him with each reception of the Eucharist. It all comes around full circle. My goodness, I should really get to Mass more often.
Peace and prayers,