God threatens to punish all who sin against these commandments. Therefore, we should fear His wrath and not act contrary to these commandments. But He promises grace and every blessing to all who keep these commandments. Therefore, we should also love and trust in Him and gladly do what He commands. (Small Catechism: Explanation to Close of the Commandments)
In the Name + of Jesus. Amen. In the book of Exodus, when God gave Moses and Israel the Ten Commandments, He spoke these words right after the First Commandment: "I, the Lord your God, am a jealous God, visiting the iniquity of the fathers upon the children to the third and fourth generations of those who hate Me, but showing mercy to thousands, to those who love Me and keep My commandments."
By placing this Bible passage and explanation at the close of the Ten Commandments, Martin Luther makes the First Commandment the bookend to this section of the Small Catechism. It's easy to see why. Wherever the First Commandment is broken, so are the others. And wherever any other commandment of God is broken, it leads us back to the First Commandment. It's also a reminder that though we sin against our friends, family, and neighbors, we also sin against God. And the wages of sin is death.
The close of the Ten Commandments is one more reminder of why God gives us the Law. It wasn't for us to earn His love, or for us to climb the stairway to heaven. Rather, God speaks His Word of Law to show us our sin, and our need for salvation in Jesus. Jesus crucified and risen is our hope in the face of the Law's punishment and God's wrath for our sin. Jesus perfectly kept God's Law for you. Jesus was obedient for you. Jesus was judged for you. Jesus bore God's wrath for you. "Therefore, we should also love and trust in Him and gladly do what He commands." In the Name + of Jesus. Amen.
Our works cannot salvation gain; They merit only endless pain. Forgive us, Lord! To Christ we flee, Who pleads for us endlessly. Have mercy, Lord! (These Are the Holy Ten Commands, LSB 581:12)