The Divine Service’s pattern of reading from Scripture follows that of the Jewish synagogue experienced by Jesus and the apostles.
Today the First Reading is usually, but not always, taken from the Old Testament. When the early Christians moved from meeting in synagogues to house churches they listened to not one, but three Old Testament readings, plus Epistle and Gospel lessons.
Historical evidence indicates that the Old Testament was read during worship up until the sixth century to eighth centuries (depending on region), at which time the Old Testament was dropped. It wasn’t added back into the Western Church’s lectionary with any success until the twentieth century when the three-year reading series was introduced as an alternative to the one-year series.
The text of the first reading is meant to relate to the day’s Gospel lesson, however, occasionally it will stand on its own. (Matt. 4:23; 13:54; Matt. 23:6; Mark 1:21; Acts 17:11)