This is a semantic investigation of spirituality in ancient Israel as mirrored in the Book of Isaiah. Particular attention is given to the concept of faith in Yahweh. There are two main approaches. Firstly, verbs describing man's relation to Yahweh are studied according to the semantic fields of Attention, Emotion, Motion, religious Acting and Consummation. Secondly, divine epithets used for confessions to Yahweh are studied according to their semantic Divine Terms, Ethical Terms, Creation Terms, Royal Terms, Military Terms, Anthropological Terms, and Family Terms. Both the verbs and the divine epithets are studied in relation to their semantic fields and in their context, followed throughout the whole Book of Isaiah, and summarised according to the main units of as well as the complete Book of Isaiah. The intention is to find how the vocabulary of the Book of Isaiah reflects the spiritual life of ancient Israel in the 8th and 6th century BC - and later.