10 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.

Read Ezra 7:10 Using Other Translations

For Ezra had prepared his heart to seek the law of the LORD, and to do it, and to teach in Israel statutes and judgments.
For Ezra had set his heart to study the Law of the LORD, and to do it and to teach his statutes and rules in Israel.
This was because Ezra had determined to study and obey the Law of the LORD and to teach those decrees and regulations to the people of Israel.