The aim of your sermon is to help God’s people understand the main purpose of the old Mosaic covenant, and how it relates to the covenant made with Abraham and fulfilled in Christ. Having done so, you will explain how we are meant to handle/interpret old covenant law. Give particular emphasis to the fact that there are not two people of God (Israel and the Church), but one people, those who have faith in Jesus Christ.
15 To give a human example, brothers: even with a man-made covenant, no one annuls it or adds to it once it has been ratified.