Universalism is not a teaching of the Catholic Church.
Having said that, from the very beginning of Christian history the notion of universalism – by which I mean the notion that God will restore
all humankind (and even all spirit creatures, according to some) in the “life in the age to come” (from last words of our creed) – has been embraced and advocated by many of the faithful. Even to this very day.
It would be wrong to say the Church teaches universalism. It doesn’t. However, it is not wrong to
hope that God will ultimately restore all humankind in accordance with His will and mercy, the fulness of which we cannot grasp. There’s a world of difference, and it is in the space between the differences that I believe the debate over universalism hurls off the rails.
A
universalist hope is really about an abiding faith in God’s character, particularly in His immeasurable abundance of love, mercy, and grace, especially as revealed in the person of Jesus Christ. Such faith in God’s character accords with Church teaching.
God “desires all men to be saved…” (Catechism, 74; emphasis mine)
In the course of its history, Israel was able to discover that God had only one reason to reveal himself to them, a single motive for choosing them from among all peoples as his special possession: his sheer gratuitous love. And thanks to the prophets Israel understood that it was again out of love that God never stopped saving them and pardoning their unfaithfulness and sins. (Catechism, 218; emphasis mine)
And of course there is the witness of Scripture to God’s “gratuitous love” and mercy:
Merciful and gracious is the Lord, slow to anger, abounding in mercy. He will not always accuse, and nurses no lasting anger; He has not dealt with us as our sins merit, nor requited us as our wrongs deserve. For as the heavens tower over the earth, so his mercy towers over those who fear him. (Psalm 103:8-10; emphasis mine)
For as the heavens are higher than the earth, so are my ways higher than your ways, my thoughts higher than your thoughts. (Isaiah 55:9)
God is love. (1 John 4:8)
In the beginning was the Word, and the Word was with God, and the Word was God. … And the Word became flesh and made his dwelling among us, and we saw his glory, the glory as of the Father’s only Son, full of grace and truth. (John 1:1,14)
There are numerous other passages that could be quoted (including other passages relating to God’s character of justice, righteousness, etc.). But suffice it to say that, albeit we have the treasure of the revelation of God in Christ, our limited human understanding nonetheless cannot fully grasp the limitlessness of God and His mercy, the expressions and manifestations of which often surprise us (and sometimes contrary to our established understanding). This is where
universalist hope resides. Such
hope is ultimately an assertion of faith in, and appeal to, the boundless mercy and “gratuitious love” of God, and such faith does not contradict nor seek to misrepresent or supplant the established teaching of the Church per the Magesterium (see Catechism, 93-95).
The Christian economy, therefore, since it is the new and definitive Covenant, will never pass away; and no new public revelation is to be expected before the glorious manifestation of our Lord Jesus Christ.” Yet even if Revelation is already complete, it has not been made completely explicit; it remains for Christian faith gradually to grasp its full significance over the course of the centuries. (Catechism, 66; emphasis mine)