The following comes from:
Ali Bonner, The Myth of Pelagianism (British
Academy Monographs; Oxford: Oxford University Press, 2018), 8
[Pelagius] drew a distinction between eternal life and the kingdom of
heaven in so far as he wrote that there were many mansions in heaven, and that different
levels of goodness would receive different levels of reward in the afterlife.
This was expressed in his letters when he wrote about the vocation to
virginity, and it appears to have been intended as a means to differentiates
the special reward given those who dedicated themselves as virgins. [24] It
would perhaps have afforded room somewhere for unbaptised infants . . .
[24]
Pelagius, Ad Demetriadem 17 (ed. Greshake, p. 118), ‘In the kingdom of
heaven there are different dwelling-places according to an individual’s merit’;
‘Dispares sunt in regno coelorum pro singulorum merito mansiones.’