Jamin was one of the many Levites who assisted Ezra in explaining and making clear the law to the people, so that they could understand it. The others were Jeshua, Bani, Sherebiah, Akkub, Shabbethai, Hodijah, Maaseiah, Kelita, Azariah, Jozabad, Hanan, and Pelaiah. Interestingly Jamin in Hebrews means right hand. When the people understood the words, they first wept and then upon counsel from Nehemiah, Ezra and the Levites such as Jamin, they understood that the Joy of the Lord was their strength and they celebrated with great joy (Nehemiah 8:12).

What can we learn from Jamin?
We must be like Jamin, a right hand to those who are pastors and preachers (like Ezra), in explaining and making clear the Scripture, so that the people who hear it can understand it. For when they understand it, they will recognize the grace of God in Christ Jesus and weep in repentance, following which they will be filled with the Joy of the Lord in Christ Jesus.

Nehemiah 8:7 (KJV)
7 Also Jeshua, and Bani, and Sherebiah, Jamin, Akkub, Shabbethai, Hodijah, Maaseiah, Kelita, Azariah, Jozabad, Hanan, Pelaiah, and the Levites, caused the people to understand the law: and the people stood in their place.
8 So they read in the book in the law of God distinctly, and gave the sense, and caused them to understand the reading.
9 And Nehemiah, which is the Tirshatha, and Ezra the priest the scribe, and the Levites that taught the people, said unto all the people, This day is holy unto the LORD your God; mourn not, nor weep. For all the people wept, when they heard the words of the law.
10 Then he said unto them, Go your way, eat the fat, and drink the sweet, and send portions unto them for whom nothing is prepared: for this day is holy unto our LORD: neither be ye sorry; for the joy of the LORD is your strength.
11 So the Levites stilled all the people, saying, Hold your peace, for the day is holy; neither be ye grieved.
12 And all the people went their way to eat, and to drink, and to send portions, and to make great mirth, because they had understood the words that were declared unto them.