There are in the Bible ‘fools’ who do not believe in God (Ps. 14: 1), not on the ground of considered rational argument but by reason of their depraved and selfish lives. The atheism therefore of modern existentialists like Jean-Paul Sartre or positivists who maintain that we have access to knowledge only through the empirical sciences is unknown to the OT and NT alike. God was, is, and is to be (Exod. 3: 14); the Hebrew verb denotes habitual manifestation. This is the first revelation in the E source of the Pentateuch of the divine name, and it implies that our concept of existence is too limited, but God is known when he makes himself present to people and they respond.
God in the Bible is conceived as the absolutely good creator of everything that exists. As in other religions it is expected that devotion to God will bring personal and national well-being and avoidance of calamity. This devotion consists in a prescribed way of life, such as eating certain foods, which give the community a sense of solidarity. In the OT the Torah (Law) contains a code of ritual and ethical behaviour and it is held that these come direct from God. So for Israel belief in God necessarily means also participating in the life of the community and its rites.
The Hebrews did not arrive at their monotheism without a long gestation—from a polytheistic environment, via henotheism (when Israel worshipped one God but admitted the existence of other peoples' gods, as is implied by Deut. 5: 7), to an ethical monotheism. A distinction between Yahweh and other gods which began in the 9th cent. BCE was sharpened by Hosea in the 8th cent. In the 7th cent. (Deut. 13: 6–11) faithful Israelites are to inform on relatives who worship other gods. By the time of the Exile, belief in Yahweh as sole God, author of both good and evil, is accepted by Deutero-Isaiah (Isa. 45: 7). Yahweh is regarded as Creator of the world but also as the supreme being who has graciously entered into a covenant with his people. Images which describe God are king, father, and shepherd: masculine in gender, but later literature in which the personified wisdom reveals God shows that the feminine is not alien to OT conceptions of God—since the Hebrew for ‘wisdom’ is feminine; and God's activity is sometimes described in terms of female characteristics (Isa. 66: 13).
God who is transcendent is also a God who condescends to dwell in the midst of his people. It was a Hebrew belief that the divine presence ‘tabernacled’ among them and in due course dwelt in the Temple. He was regarded as a God who demanded righteousness and justice and his wrath could be poured out on those who disobeyed him.
This contrast between OT and NT was overdrawn by the heretic Marcion (c. 150 CE), and the Christian Church has always maintained that the God of Israel, the Father of Jesus, is the God whom Christians also worship. There is a continuity of concept. However, the fundamental change brought to the biblical concept of God was that for Christians the main place in which God reveals himself was now in Jesus the Christ (Matt. 1: 23; John 14: 9). God in the NT remains the holy, transcendent God of the OT but it is believed that Jesus has shown in a human life that fundamentally God is love. Christian experience led further to the doctrine of the Trinity, of which there are already hints in the NT (e.g. Matt. 28: 19). For Paul's language about believers' participation in the Spirit (2 Cor. 13: 13) is possibly spelt out by the later formulated doctrine of the Spirit as a distinct ‘hypostasis’ (‘Person’) within the very being of the Godhead.
Several names are given to God in the Bible. The Hebrew EI is often used in the plural Elohim. He is contrasted with the heathen Baal in the Deuteronomist history and in Hos. 2. Yahweh occurs nearly 6,000 times in the OT, but in the Masoretic text (6th cent. CE) the vowels of Adonai (‘my Lord’) were inserted into the ineffable name Yahweh, hence the English Jehovah. The phrase Yahweh Sabaoth (= Lord of hosts) is found 279 times in the OT, especially frequently in the prophets; originally the reference was to hosts of war but came to mean the powerful functions of Yahweh in command of nature and the fortunes of men. The NT never denies the holiness of God (much emphasized in the OT) but prefers to use expressions referring to his faithfulness (1 Cor. 1: 9), wisdom (Rom. 16: 27), truth (John 3: 33). He is the God of peace (1 Thess. 5: 23), hope (Rom. 15: 13), and above all love (2 Cor. 13: 11; and John 3: 16; 1 John 4: 8).
The biblical concept of God as almighty (e.g. Matt. 26: 53), and that his omnipotence can intervene directly in the affairs of this world, must be modified nowadays by the recognition that there is a limit imposed on divine omnipotence in that the universe operates predictably and this is a necessary foundation for human freedom and responsibility. The power of God can be conceived as that of suffering love, of self-emptying which actually gives power to what is created over its creator. God does act in the world (as the Bible maintains) but more in the sense that he has created a world of order, value, and rationality—through which we can conceive of the idea of deity and of human existence lived in credibility and obedience to a God of love. Neither OT nor NT offers arguments for theism; rather their narratives are compelling illustrations of the life of faith.