The prophet Amos leans on his shepherd’s crook, a mark of his vocation before he became a prophet in the mid-eighth century B.C.E. Portrayed here with an uncompromising gaze that recalls the character of his prophecies, Amos warned of God’s anger and judgment as he sternly criticized the corrupt and indulgent social order of his day. He probably did not live to see his prophecy fulfilled in 721 B.C.E., when the Assyrians conquered the northern kingdom of Israel.

Amos was one of the “writing prophets,” a designation that includes Isaiah, Hosea and Micah, who practiced a new style of prophetism in the eighth century. In contrast to the courtly prophets who preceded them, the “writing prophets” addressed the whole people and spoke of social concerns. Moreover, they or their scribes actually wrote their prophecies, using the language of sublime poetry, a development that parallels the general growth of literacy at the time. Why this new kind of prophetism arose when it did, however, remains a major mystery.

John Singer Sargent’s “Frieze of the Prophets,” of which Amos is a detail, also shows 16 other Old Testament prophets. Commissioned in 1890, it decorates a hall in the Boston Public Library. The 38-foot-long, 7-foot-high oil painting in five panels lines the walls about 10 feet above eye level and portrays the prophets slightly larger than life.