The Lectionary is a system of Bible readings selected to portray, week by week and by celebration of special festivals (on Sundays and other days), the life and ministry of Jesus Christ, the Savior of sinners. The readings from the Old Testament recall and proclaim the promises of God to send a Savior; the readings from the Gospels testify and proclaim how God kept all these promises in Christ (2Cor 1:20). The readings from the Epistles (letters of the New Testament) explain and apply the doctrine (teaching) of God’s Word to our daily life.
Trinity uses the “Three-Year Lectionary,” which is currently in 2018-2019 Series C (using primarily the Gospel according to St. Luke). Here is a link to the Lutheran Church Missouri Synod Church year calendars.