The prophet Isaiah is the key prophet of the Old Testament. Except for the Psalms, the prophet Isaiah is the longest book of the Old Testament. This year, all four of the first readings during the season of Advent, as well as many daily Mass readings come from the book of the prophet Isaiah. The Orthodox Christian Church even celebrates Saint Isaiah on May 9. Why is he so important? First, his prophecy is grounded in a powerful relationship with God. The vision we hear described at the start of the book of Isaiah forms the foundation for everything he says. Second, he is able to read the signs of the times. While he was surely politically astute, his message is consistent. Trust in God. Third, Isaiah recognizes and challenges people to see that sincere faith in God impacts the behaviors of our lives. Lastly, it is easy to see in the prophecies of Isaiah a foreshadowing of the life of Jesus and the arrival of the Messiah.