Ezra had devoted himself to the study and observance of the Law of the Lord, and to teaching its decrees and laws in Israel

 Ezra 7:1-28

After these things, during the reign of Artaxerxes king of Persia.

Ezra came up from Babylon. He was a teacher well versed in the Law of Moses, which the Lord, the God of Israel, had given. The king had granted him everything he asked, for the hand of the Lord his God was on him. Some of the Israelites, including priests, Levites, musicians, gatekeepers and temple servants, also came up to Jerusalem in the seventh year of King Artaxerxes.

For Ezra had devoted himself to the study and observance of the Law of the Lord, and to teaching its decrees and laws in Israel.

You and your fellow Israelites may then do whatever seems best with the rest of the silver and gold, in accordance with the will of your God. Deliver to the God of Jerusalem all the articles entrusted to you for worship in the temple of your God. And anything else needed for the temple of your God that you are responsible to supply, you may provide from the royal treasury.

And you, Ezra, in accordance with the wisdom of your God, which you possess, appoint magistrates and judges to administer justice to all the people of Trans-Euphrates—all who know the laws of your God. And you are to teach any who do not know them. Whoever does not obey the law of your God and the law of the king must surely be punished by death, banishment, confiscation of property, or imprisonment.

Why?
Devote himself, study, and observance of the Law of the Lord, teaching its decrees and laws in Israel.

Under the King's letter, Ezra can do anything good to worship the Lord and reach the word of the Lord in Jerusalem.

The Lord through King of Persia, Artaxerxes, gives a letter to all Israelites in his kingdom. And he has the authority to use financial support from the royal treasury.

How?

The Lord is the master of Christians and non-Christians. God's power over all in the world.