"If, as (F.D.E.) Schleiermacher suggests [in Christian Faith, 1821-2], the distinctive essense of Christianity consists in the fact that God has redeemed us through Jesus Christ, and through no one else and in no other way, it must follow that the Christian understanding of God, Jesus Christ, and human nature should be consistent with this understanding of redemption. Thus the Christian understanding of God must be such that God can effect the redemption of humanity through Christ; the Christian understanding of Christ must be such that God may effect our redemption through him; the Christian understanding of humanity must be such that redemption is both possible and genuine. In other words, it is essential that the Christian understanding of God, Christ, and humanity is consistent with the principle of redemption through Christ alone.- Christian Theology, Alister McGrath, P.153
According to Schleiermacher, the rejection or denial of the princple that God has redeemed us through Jesus Christ is nothing less than the rejection of Christianity itself. In other words, to deny that God had redeemed us through Jesus Christ is to deny the most fundamental truth claim which the Christian faith dares to make. The distinction between what is Christian and what is not lies in whether this principle is accepted. The distinction between what is orthodox and what is heretical, however, lies in how this principle, once conceded and accepted, is sunderstood. In other words, heresy is not a form of unbelief; it is something that arises within the context of faith itself. For Schleiermacher, heresy is fundamentally an inadequate or inauthentic form of Christian faith."
According to Schleiermacher, then, are Gnostics heretics or unbelievers? I'm still a little unclear on the role Christ was to play. +Rev. Hoeller has a description here, but I'm not sure how that applies to Schleiermacher's definitions.