Paul again appealed to the Law to show that what he had written in Romans 13:8 was in harmony with what God had commanded earlier. Whereas the Mosaic Law specified numerous situations in which the Israelites were to practice love, the Law of Christ contains comparatively few. The simple principle is enough. This is another excellent example of the essentially legal character of the Mosaic Law and the gracious character of Christ"s teachings. Jesus Christ gave us a model to follow in loving ( John 13:34). Love promotes obedience. [source][source][source]
"The Christian, who belongs to the New Covenant people of God, is no longer "under the [1] law," the law for the Old Covenant people of God; he is under a "new law," "the law of Christ" (see Galatians 6:2 and 1 Corinthians 9:19-21). And central to this new law is a command that Christ himself took from the Mosaic law and made central to his new demand: the command to love our neighbors as ourselves (cf. Galatians 6:2 with Romans 5:13-14)." [2][source]
"What is commanded is that we are to have the same loving regard for others that we have instinctively for ourselves." [3][source]