The readings for Pentecost 13 are taken from Isaiah 51:1-6; Romans 11:33—12:8; and Matthew 16:13-20.
Today’s lessons follow last week—God continues to make clear that His people, the true children of Abraham, are those souls regenerated by His Word and Spirit (all human nature is corrupt the same and thus foreign to God). God’s people, then and now, wait for and look to God for encouragement as we wait for Him to complete His redeeming work in us and among us.
Isaiah comforts the genuine children of Abraham. Notice the language about our relationship with God: those who follow (see John 10), you who seek, hewn from the Rock. As surely as God began His redeeming work in your life, so surely He will complete it.
Paul reminds the Romans of the riches of God’s goodness toward us, and then begins the last chapters that describe the power of that goodness at work in us. By the mercies of God, we live according to His design and will during our sojourn in this world, in this body.
Matthew records Jesus distinguishing between the chatter of people about who He was from the truth of who He was. That truth is that Jesus fulfills every promise of God in the Old Testament by demonstrating and completing His redeeming work among those who were finding rest in honesty about dependence on Him. Again, as surely as God gave rest to the faithful during the Babylonian captivity, so surely God brings us to rest.