LSB's Altar Book contains a listing of invitatories to be spread across the post-Trinity season in both Matins and Morning Prayer. I never paid much heed to them at first. Now I note to my surprise that the first four of the series have a familiar ring:
Trinity: The Lord has called us by the Gospel.
Trinity 1-8: The Lord has gathered us in the true faith.
Trinity 9-13: The Lord has enlightened us in the true faith.
Trinity 14--20: The Lord has sanctified us in the true faith.
Trinity 20-24: Glorious is God with His angels and saints.
Trinity 25-27: The Lord will come again in glory.
Yup. Right out of the Catechism's explanation to the Third Article. Which makes those four invitatories addressed, rather interestingly, to the Holy Spirit, the Lord and Giver of life. He is the Lord who calls us by the Gospel, gathers, enlightens, and sanctifies us in the true faith. Note that the fifth invitatory falls generally between St. Michael and All Angels and the feast of All Saints. The last invitatory falls during the time devoted to the second coming of our Lord in the Sunday lectionary.
A unique interplay then of lex orandi and lex credendi here, and we see how they are but two sides of one coin. I think it was Sasse who said something along the lines that a doctrine that cannot be prayed is no doctrine at all.