The love is the grace of God
The commandments given by Moses constitute the natural Law of man. In other words, we understand by natural law those laws that we naturally understand by the use of reason, for example we all understand the meaning of the precept "you will not steal."
Aristotle talks about the natural law, in his book Rhetoric, Book I, Chapter XIII:
"The just and the unjust have already been defined with reference to two laws, and in two ways, according to who is verified. Now, I divide the law in particular and in common: in particular, that wich is established for each people with respect to itself, and it is partly unwritten, and partly written, common is the law according to nature, because according to this there is something commonly fair and unfair, which everyone guesses, even if there is no common agreement between one and other peoples, nor any agreement; just as Antigona is presented to us in Sophocles, when she says that it is fair to bury Polynices, whose burial was prohibited, as this is fair by nature, "because this is not now, nor yesterday, but it always existed, and nobody knows where it comes from". And as Empédocles says, do not kill what has life, for this is not fair to some and unfair to others."
The spiritual life, that is, the life in grace, in the other hand, is not related to the natural use of reason or the rational understanding of the laws of the human being, by the use of reason we understand that it is unfair to go against the commandments Consequently, that is why we speak of a natural law and a law of grace. The law of grace goes beyond reason and is related to redemption and the change of mind, from a life full of sins to a life of righteousness. In other words: the change of heart. That is why Paul in his letter to the Romans expresses:
"Let no debt remain outstanding, except the continuing debt to love one another, for whoever loves others has fulfilled the law. The commandments, "You shall not commit adultery", "You shall not murder", "You shall not steal", "You shall not covet" and whatever other command there may be, are summed up in this one command: "Love your neighbor as yourself". Love does not harm to a neighbor. Therefore love is the fulfillment of the law". Romans 13:8-10