Orthodox theology has commonly held that God is not subject to suffering caused by action from without, changing emotions from within, or feelings of pain or pleasure caused by another being. In Christianity there is, however, tension between the idea of the immutability, perfection, and all-sufficiency of God, which would seem to exclude all passion, and the central conviction that God in His essence is love, and that His nature is revealed in the Incarnate Christ, not least in His Passion. Some modern theologians therefore question whether it is legitimate to speak unreservedly of God's impassibility. In the 20th cent. Divine impassibility was challenged by philosophers as incoherent, by Process theologians as a relic of an outmoded metaphysics, and by J. Moltmann and others as a blasphemous irrelevance in the light of modern suffering under totalitarian regimes.