Isaias was a member of a junior clan of the house of David, dwelling in Jerusalem in the age when the ferocious imperialism of Assyria overwhelmed first the north, then the centre of the Israelite peoples, and menaced little Judah when it remained the sole remnant of the tribes that Moses had led out of Egypt. His work was to be the spiritual guide and prophet of its survival; to be ascribed solely to deep faith in God, at the same time as he announced the doctrine of the Incarnation to men. But his prophetic office also involved a spiritual development in his own soul, which can here be traced as far as the records permit.