There is an assumption that this is a new idea. Something modern liberal theologians cooked up. Not so.
Apokatastasis was a major part of Christian theology in the early church.
The main Patristic supporters of the apokatastasis theory, such as Bardaisan, Clement, Origin,
Didymus, St. Anthony, St. Pamphilus Martyr, Methodius, St. Macrina, St. Gregory of Nyssa (and probably the
two other Cappadocians), St. Evagrius Ponticus, Diodore of Tarsus, Theodore of Mopsuestia, St. John of Jerusalem,
Rufinus, St. Jerome and St. Augustine (at least initially) … Cassian, St. Issac of Nineveh, St. John of Dalyatha,
Ps. Dionysius the Areopagite, probably St. Maximus the Confessor, up to John the Scot Eriugena,
and many others, grounded their Christian doctrine of apokatastasis first of all in the Bible.
— Ramelli, Christian Doctrine, 11.