The way of the Cross is the way of suffering.
It makes me happy to be suffering for you now, and in my own body to make up all the hardships that still have to be undergone by Christ for the sake of his body, the Church. (Col. 1:24, NJB)
According to St. Paul, there are afflictions (the word used by the NIV) still to be suffered by Christ for the sake of the Church! But wait a second. We know that Christ’s sacrifice on the Cross paid the entire price of our sins. What then can St. Paul mean when he says something here that sounds suspiciously different? The Navarre Bible proposes this:
The most common explanation of this statement is summarized by St. Alphonsus as follows: “Can it be that Christ’s passion alone was insufficient to save us? It left nothing more to be done, it was entirely sufficient to save all men. However, for the merits of the Passion to be applied to us, according to St. Thomas … we need to cooperate (subjective redemption) by patiently bearing the trials God sends us, so as to become like our head, Christ. (Thoughts on the Passion, quoted in St. Paul’s Captivity Letters, p. 142; emphasis added)
This is why the way of the Cross is the way of suffering: we cooperate with God by patiently bearing the trials He sends us. St. Alphonsus refers to the teaching of Aquinas on this subject, which we find here:
As stated above (1, ad 4,5), in order to secure the effects of Christ’s Passion, we must be likened unto Him. Now we are likened unto Him sacramentally in Baptism, according to Romans 6:4: “For we are buried together with Him by baptism into death.” Hence no punishment of satisfaction is imposed upon men at their baptism, since they are fully delivered by Christ’s satisfaction. But because, as it is written (1 Peter 3:18), “Christ died” but “once for our sins,” therefore a man cannot a second time be likened unto Christ’s death by the sacrament of Baptism. Hence it is necessary that those who sin after Baptism be likened unto Christ suffering by some form of punishment or suffering which they endure in their own person; yet, by the co-operation of Christ’s satisfaction, much lighter penalty suffices than one that is proportionate to the sin.
We must suffer this “lighter penalty” because we sin after Baptism. This is not inconsistent with what is said in Hebrews:
My son, do not scorn correction from the Lord, do not resent his training, for the Lord trains those he loves, and chastises every son he accepts (12:5-6, NJB)
So we must suffer.
That is not to say that it is in any way a fun thing. Again, Hebrews says any discipline is at the time a matter for grief, not joy (12:11). That is why the word is suffer. We cannot escape this, and we really shouldn’t try. Obviously we do not have to seek suffering out, and it is rational to seek relief, but the wisdom of God is foolishness with men: we benefit from our suffering, whether we can see that or not. We believe it because God says it. So I need to bear my trials with patience, because in this way I am united to my Savior and God. It is necessary, as we recently learned.