For as the child new-born is free from accusations and from penalties, so too the child of regeneration has nothing for which to answer, being released by royal bounty from accountability. And this gift it is not the water that bestows (for in that case it were a thing more exalted than all creation), but the command of God, and the visitation of the Spirit that comes sacramentally to set us free. But water serves to express the cleansing. For since we are wont by washing in water to render our body clean when it is soiled by dirt or mud, we therefore apply it also in the sacramental action, and display the spiritual brightness by that which is subject to our senses. (Oration on the Baptism of Christ)
So was Gregory a paedobaptist? He here seems to deny original sin and guilt, which lead Augustine to conclude infant baptism should be required (even though Augustine’s christian mother did not baptize him). In the Great Cathechism, Gregory writes:
Baptism is a spiritual birth, but he who is born by spiritual birth must recognize by whom he is born and what kind of creature he must become. In physical birth, those who are born owe their life and existence to the impulse of their parents, but the spiritual birth is in control of the one who is being born. It is the only birth where we can choose and determine what kind of beings we are to become.
Choice and free will, recognition of God’s power to transform are part of the process of being reborn and entering baptism. In other words, Gregory of Nyssa is a credobaptist, as already demonstrated by an awesome essay I just came across by Everett Ferguson, “The Doctrine of Baptism in Gregory of Nyssa’s Oratio Catechetica” in Dimensions of Baptism: Biblical and Theological Dimensions, New York: Sheffield Academic, 2002. You can read the whole essay on Google Books!