Jesus says that all of the Law and the Prophets hang on the two greatest commandments: loving God with the totality of your existence and loving your neighbor as yourself. That all sounds good, but what is meant by this notion of the Law and the Prophets?
To begin with, we ought to make it clear what this passage is not saying. It is not saying that the Law and the Prophets have all been derived from these two commandments (just the opposite — these two commandments are a summary of the Law and the Prophets!). Further, this is not saying that if you do these two commandments, you are able to fulfill all that the Law and the Prophets demand (as if we could do this fully!).
To begin with, the Law, when spoken in a context like this, is most typically a reference to the Pentateuch, or the first five books of the Bible — known as the Books of Moses or the Torah (the Hebrew word for Law). The Prophets refer to the books of Joshua, Judges, Samuel, Kings, Isaiah, Jeremiah, Ezekiel, and the Twelve Minor Prophets — again, this is a Hebrew designation for these works.
What function do these books play? To begin with, they introduce the Law and the Covenant to the people of God. Second of all, they demonstrate the failure of the people of God to fulfill the righteous demands of the Covenant Law and of God’s faithfulness to his Covenant promises despite the people’s failures. In a very real sense, the purpose of the Law and the Prophets was to communicate to the people that they did not fulfill the Law and the Prophets (in most cases, they didn’t even try) and to demonstrate to the people that they needed a redeemer.
There is a telling passage that speaks to this reality found in Ezekiel 7:26. Ezekiel has been prophesying the destruction of the land of Israel and in that context, he says that the Law has perished from the priests (they no longer honor it or preach it to the people) and the people seek visions from the Prophets (yet the prophets make no sense apart from the Law). So, what do the people have but judgment and terror?
In the Sermon on the Mount, Jesus states unambiguously that he has come to fulfill and not abolish the Law — that the Law will never pass away until the heavens and the earth pass away. Indeed, in coming as the new and greater Covenant mediator, who can live out the Law perfectly on behalf of his people, he also fulfills the Covenant that God made and the people broke. In fact, Christ is the great fulfillment of this Covenant promise, the beginning of which is found in Genesis 3:15.
So, what is this ultimately saying to us? To begin with, Jesus is the demonstration of what it looks like to live out the first and second “greatest” commandments perfectly. If we wish to grow in grace and in spiritual maturity (as well as in demonstrating our Love toward God), this is that for which we must strive. Second, it is a reminder that without a love of God (that emanates from the totality of our being), we don’t even have a chance of living out the second (which flows from the first). We love our neighbor not as an individual command in and of itself; we love our neighbor because we love our God — the second flows out of the first. And third, if you could summarize the Law and Prophets — what God expected of his people and what his people failed to do — then here you have it: Love the Lord your God with all of your heart, with all of your soul, with all of your mind, and with all of your strength, and love your neighbor as yourself.