What happened between the Old and New Testament that led to significant changes in religious beliefs and practices?

The period between the Old and New Testament saw the rise of Hellenistic influence and the spread of Greek culture. This led to changes in religious beliefs and practices, including the development of new ideas and the blending of different traditions. Additionally, the destruction of the Second Temple in Jerusalem in 70 CE marked a significant turning point, leading to the emergence of new religious movements such as Christianity.