Wellhausen used the sources of the Torah as evidence of changes in the history of Israelite religion as it moved (in his opinion) from free, simple and natural to fixed, formal and institutional.[39] Modern scholars of Israel's religion have become much more circumspect in how they use the Old Testament, not least because many have concluded that the Bible is not a reliable witness to the religion of ancient Israel and Judah, representing instead the beliefs of only a small segment of the ancient Israelite community centred in Jerusalem and devoted to the exclusive worship of the god Yahweh.[40][41]