The priest who initiated the process of developing the canon when he joined one of the groups of Israelites who returned to Jerusalem from their captivity in Babylon.

The priest you're referring to is Ezra. Here are the steps that led to his significant role in developing the canon:

1. The Israelites were exiled to Babylon after the Babylonian conquest of Judah. This period is known as the Babylonian captivity.

2. After several decades, the Persian Empire, under King Cyrus, conquered Babylon. Cyrus issued a decree allowing the Israelites to return to Jerusalem and rebuild their temple.

3. Among the groups of Israelites who returned to Jerusalem was a priest and scribe named Ezra.

4. Ezra was a learned man who had studied the Law of Moses extensively. He was deeply concerned about the spiritual state of his people and their neglect of the Law.

5. Ezra took the initiative to gather the people in Jerusalem and read the Law to them. This event was significant because it marked a renewed commitment to the Law among the Israelites.

6. Ezra didn't stop at merely reading the Law. He also took steps to interpret it and apply it to the contemporary context. This process of interpretation and application is what we refer to as "developing the canon."

7. Ezra's work laid the foundation for the later development of the canon of the Hebrew Bible. His efforts to teach the Law and apply it to everyday life helped to establish the authority of the written text, which was a crucial step in the process of canonization.