Adimpleo ea quæ desunt passionum Christi, in carne mea pro corpore ejus, quod est Ecclesia.
In my flesh I am filling up what is lacking in the afflictions of Christ on behalf of his Body, which is the Church...
You have to admit that's a shocker.
Paul, who is not God, saying his pains somehow complete what is lacking in Christ's afflictions? The Greek word rendered in Latin as "desunt" is ὑστέρημα, husteréma, meaning "lacking" but also "a defect". It's a strong word here.
The Anglicans, contra St Paul's divinely inspired teaching, underscore what most of us modern folks (I dare say, many Catholics as well) would understand as the truth, that Christ on Calvary, made "by his one oblation of himself once offered a full, perfect, and sufficient sacrifice, oblation, and satisfaction, for the sins of the whole world". We'll get into the daily, omnipresent Eucharistic Oblation at another time, but today let's let the Anglican formulary (and what I presume is the understanding of most modern folks about Jesus' actions) wrestle with St Paul's idea that he can add something to Jesus' sufferings.
Follow me here.
Jesus says: Whatever you do to the least of these, my brethren, you do to me.
Paul says: For as many of you as have been baptized in Christ, have put on Christ...and are made one in Christ.
Jesus goes further and says: As the Father has loved me (which love we understand to be the Holy Spirit) so have I loved you; and we are also to love one another.
Even Cramner says that in the Eucharist we are made "very members incorporate in the mystical body of" Jesus.
By Baptism and Eucharist, by our incorporation into the Body of Christ, we participate fully in the death and resurrection of Jesus. We do not thereby exhaust the power of God in those actions (which is infinite) but rather make those actions present in place and time. Our simple somatic presence in this world is replaced by God's divine Zoe, the life of Christ.
What happens to us - in that state of Grace - is part of the Passion of Christ.
And all of our lives, if properly offered to God, can partake of that divine transaction.
Thus our suffering - our back pains, our arthraticky, our lumbago, our agony over the place of America in the world, our wrestling with the ideas of the current political climate, our pain at feeling rejected for our faith, our humility in submitting to an unjust boss or landlord, our willingness to go without so that our children might not go hungry, our setting aside a former life, our chastity, our abstention from meat or any other thing that is good by itself, our pains of withdrawals, our doing without an extra vacation or winter coat so that others might have one winter coat... these are now all become the action of Christ in his redemption of the World if they are offered up in that way, apud Josephum per Mariam ad Jesum
Dearest Jesus, after the example of the Chaste Heart of Joseph and through the Immaculate Heart of Mary, I offer thee all of my plans, dreams, and intentions, all of my thoughts, words, and deeds, all of my joys and sufferings, my hopes and fears, all of my crosses and crowns of this day and all of my life, all for the intentions of thy Sacred heart, in union with the Holy Sacrifice of the Mass, for the salvation of souls, the reparation of sins, the reunion of all Christians, and the intentions of our Holy Father, the Pope.