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.
Luther's 1537 statement of the articles he considered non-negotiable, written when a general council seemed likely. Blunter than the Augsburg Confession, and deliberately so.
In The Confessions — The documents collected in the Book of Concord.