As long as the commands to love God and the neighbor are classified as demand and threat – that is, the second use of the law – a contradiction exists between the gospel and the fulfillment of the command to love as the chief content of the Scriptures. This contradiction is resolved in the person of Jesus…and also is capable of a trinitarian resolution. Commands to love God and neighbor cannot be isolated from love as the fundamental unity by which the three persons of the Trinity are bound to each other (Jn 15:9-10, 12-13; 17:24). This love in which the Father and the Son and the Holy Spirit exist motivates and expresses itself in the incarnation and redemption and gives form to the gospel’s content (Jn 3:16). In loving God we are to have the same attitude which the three divine persons have among themselves and which they have as Trinity toward us. Thus the command to love God or the neighbor is not simply an arbitrary regulation, the most important law, or a summary of all laws with their prohibitions and threats. Love belongs to God’s trinitarian life, and the command to love is an invitation to participate in this love of the Trinity. Jesus’ command to love God is an invitation to believe in Him who Himself is love, and on that account God can be approached only in love rather than with fear over impending wrath for our transgressions. The command to love creates ex nihilo what it demands. This the first two uses of the law cannot do. Our ability to love God is contained in the command itself and so it comes not from within ourselves but from God. Loving God is not something in addition to faith or a superior form of faith but describes faith’s total devotion to God. Jesus’ three questions to Peter about whether he loved Him had to do with faith (Jn 21:17-19). With his affirmative responses, “Lord, you know everything; you know that I love you,” Peter was following the commands of Jesus to love God by putting his total trust in Him.
“Confessional Lutheran Dogmatics: Law and Gospel and The Means of Grace”, pages 74-75