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.
Both the inward sense of vocation and the formal, documented invitation from a congregation or synod to serve. Lutherans have generally trusted the second more than the first.