Ezra 3:1

"When the seventh month came and the Israelites had settled in their towns, the people assembled as one man in Jerusalem." NIV translation

After a period of time in which the people went to their own towns and built their own houses, they all came together in Jerusalem. It is just before this great gathering that the prophet Haggai was sent to the leaders in order to call them to focus the people on the work of the Lord and not their own homes.

Ezra 3:2

"Then Jeshua son of Jozadak and his fellow priests and Zerubbabel son of Shealtiel and his associates began to build the altar of the God of Israel to sacrifice burnt offerings on it, in accordance with what is written in the Law of Moses the man of God." NIV translation

Ezra leaves out a portion of the events that occurred at this gathering but we see it in Nehemiah 8. This is where Ezra stood and read the Book of the Law. We see that, not only was it read, but it was put into action. 

The priests began by building the altar. This altar was a place of meeting between God and His servants and is a picture of Jesus Christ. We, likewise, need a place where we can gather with a group of God's people for worship.

Ezra 3:3

"Despite their fear of the peoples around them, they built the altar on its foundation and sacrificed burnt offerings on it to the Lord, both the morning and evening sacrifices." NIV translation

We see that this return to the things of God brought opposition from the people around them. This opposition did not stop the work and they worshiped the Lord with sacrifices. It is much the same with us today as, if you are focused on the things of God, you can expect opposition.