Apparently it was the Savior who stood before Lehi and gave him a book to read. Lehi not only read a certain portion of the book, but the Spirit of the Lord came over him. In verse 14 we learn that he was allowed to see a marvelous vision of events in the future.
The destruction of Jerusalem was a horrible vision. It would turn out that this all occurred in 587 B.C., just 13 years later. King Nebuchadnezzar of Babylon would become so outraged with the insults and disdain of King Zedekiah and his associates that he would besiege Jerusalem, tear down the temple of Solomon, destroy the walls of the city, slaughter a great many of the inhabitants and then carry away the remnants off to Babylon as prisoners. It would be the most devastating attack on Jerusalem in its entire history -- exactly as the prophet Jeremiah had predicted. However, during this vision, Lehi notices that the lives of the righteous were preserved. This came as a great relief. He felt compelled to praise God for his goodness and mercy.