On: every psalm and song in the daily prayers uses today’s English. Off: all of them use the older “thee and thou”. Until you choose, the Songs of Zechariah, Mary and Simeon use today’s English, as most churches sing them. The Lord’s Prayer and the prayers for the dying show the form most people learned.
A long Latin creed setting out the Trinity and the two natures of Christ in precise terms. Included in the Book of Concord, rarely used in worship, and traditionally read on Trinity Sunday.
In The Confessions — The documents collected in the Book of Concord.