The main character’s name is Reuven Bloom. The book was published in 2005, and was written, as mentioned in the question, Kathryn Lasky. It’s a historical fiction book. The book takes place in 1897 Russia. As with most historical novels, it focuses on a young person with a wonderful talent. The life Reuven leads is hard. His friend is drafted into the army to fight in the war.
His family is killed. All of this, according to the blurb, forces him to put away his violin - which he’s incredibly gifted at. Not to mention the fact that he’s a Jew, and in Russia in 1897, the Russian government didn’t particularly like Jews. The book chronicles his attempt to escape Russia before he too dies.