A common theme of the prophets was that God was not pleased with, did not want, did not need, the sacrifices which were rendered to him. “What to me is the multitude of your sacrifices? says the LORD; I have had enough of burnt offerings of rams and the fat of fed beasts; I do not delight in the blood of bulls, or of lambs, or of he-goats” (Isa. 1:11 RSV). It is our hearts, minds, and souls which the Lord wants. “For I desire steadfast love and not sacrifice, the knowledge of God, rather than burnt offerings” (Hos. 6:6 RSV). The Law gave sacrificial rules, to be sure, but it was misunderstood by Israel. They loved the sacrifices, they loved what it offered them, but they didn’t turn themselves through such actions to God, which is what God wanted: “They love sacrifice; they sacrifice flesh and eat it; but the LORD has no delight in them. Now he will remember their iniquity, and punish their sins; they shall return to Egypt” (Hos. 8:13 RSV). Israel had learned to love the letter of the Law, but not the Spirit, the Spirit which would have directed them to God and given them true life. In turning away from God they found themselves imprisoned by sin, mystically represented by Egypt. The purpose of the Law and the Prophets was to point to Christ, to connect the ways of the world to Christ, to slowly educate and direct Israel (and through Israel, us). It was to move us away from mere human constructs, such as worldly sacrifices, so that we can find ourselves in the Kingdom of God.
At the Transfiguration, Moses and Elijah were seen as representatives of Moses and the Prophets. At Tabor, the Apostles who witnessed the event wanted to make booths, to restrict Moses, the Prophets and Christ to the letter of their understanding; this is common for all of us. We learn something, we experience something, we try to keep it where we are at, to form booths which restrict us from the fullness of the experience, to keep to the pattern we understand and not let the depth of the mystery out. This is very human, and explains why Israel misunderstood the Law. They became so encased with the sacrifices that they thought the sacrifices were the point. They did not understand that they were to be symbols of what lay beyond them: the cross of Christ. They were tools by which God used the understanding of the time to point to the transcendent truth of the cross.
Humanity had long come to believe in sacrifice, in the need for sacrifice, to create balance in the world. Even human sacrifice was seen as a possibility, where one could be expected to sacrifice one’s beloved to God if human sin was great. Abraham misunderstood God in the same way as the rest of humanity: he believed God wanted human sacrifice, the sacrifice of Isaac, and he was willing to accept the command as he understood it because human sacrifice was common all around him. He was a man of his time and yet a man of God. This is why he could be taught, why he could be shown the error of his understanding, and so why Isaac could be saved. Through Isaac, the whole of humanity could be saved, because humanity was shown God did not need any human sacrifice to be pleased with his creation. God used the symbol of the time, the ways in which Abraham understood divinity, but took them and transformed them, helping to reveal a little of the spiritual truth contained in them. Isaac was saved and a ram was killed, showing that God is willing to move beyond human constructs, human expectations, and that what was important was the symbol contained in them. “But when the ram was killed, and Isaac was not killed, it happened thus because Isaac was a figure and not the reality; for in him was designated what was later fulfilled in Christ.” With Abraham, humanity had moved a step forward; but there was still a sense that sacrifice of some sort was important and needed, so the kind of sacrifice changed, though this too, was not what God wanted. He wanted a contrite heart, a person sacrificing their ego, their false perception of the world, so to be open to him. But God was willing to show this through symbol, through the slow education of humanity. It would move forward with the Law of Moses, where one finds much spiritual truth and power. The truth was there, so that Israel contained the message of the truth, but it was rare for the truth to be understood in its fullness, to see the Spirit which was manifested by the Law. The whole of human history, even outside of Israel, contained movements of the Spirit to direct and guide it to the Kingdom of God. Spiritual truths are found throughout the world encased by all kinds of worldly systems and misunderstanding, similar to, but not to the same level, as the truths contained in Israel and its Covenant.
It is in Christ that the fullness of revelation came to the world. As the expectation of the nations, all the spiritual truths of the world, wherever they were found, were fulfilled and shown their proper end. This is not to say they are no longer useful, no longer have value. For such truths always have value, but how they are understood has been transformed. Israel and the Temple represent the world and all that is within it: Jesus is the true high priest who offers the one true sacrifice, himself, on the cross. All the sacrifices, all the sin offerings of the Law, merely point to and typify something of Christ, and their power and strength came not from themselves, but from Christ. The physical sacrifices were not, of themselves, anything; the spirit of the sacrifices is what rendered them to be of benefit, and it was the Spirit which connected them to Christ, to let them prefigure Christ, and to allow grace flow through Israel. But their value remains, and this is why we still read of the Law and what it taught. We can be directed by the Spirit to see beyond them, to show universal truths in them, such as how they show different ways in which we can gain grace, as Origen explains the sacrifices for sins in Leviticus:
God used what humanity had given, but did not want humanity to be stuck in the way of destruction: God wanted humanity to see the foolishness of it, so that we can instead follow him in spirit and in truth. The Spirit provided the means, the power, by which many were led to the good through such human means, but the Spirit then also directed them (as we saw in the prophets) to understand the true meaning of the act. We are to circumcise our hearts to have true circumcision, we are to render ourselves in love to God to render God a true sacrifice, one which he is pleased with, one which he will take, one which he will merge with Christ so as to bring us to the resurrection in glory. The Law points to the truth, and so has the truth in it, but it is not the fullness of truth. The Law cannot be kept to the letter and have life, because the letter of the Law cuts one off from the Spirit which uses the Law for an end beyond the Law itself. And, yet, the Law, or the human constructs in which God desired to show himself, is engraced so that humanity can be led to higher and higher truths until we can be free in Christ. Thus, we are shown, in salvation history, three different eras to help show us the movement we are to take: from nature to the Law to Christ, where each level gives knowledge and grace greater than the last. Thus, Hugh of St. Victor talks about how God instituted sacraments, not just in the Church, but in all of human history:
Sacraments were instituted from the beginning for the restoration and guardianship of man, some under the natural law, some under the written law, some under grace. And among these those which have been posterior in time are always found more worthy of the effect of spiritual grace. For all of those sacraments of earlier times, whether under the natural law or under the written, were signs, as it were, and figures of those which now have been set forth under grace. And the spiritual effect which they operated in their own time when placed before these, they operated by that virtue and sanctification which they assume from these.
To properly understand the Law, to properly be directed by it, we must understand the Spirit of the Law, to understand what God saw he could use in it to direct to the fullness of truth. We must not be caught, as so many, in the letter, to think it was the sacrifices, the rules and regulations, are what mattered – in and of themselves. It was what they pointed to, Christ, which mattered, and how Christ was able to encompass them and lead us through them to eternal life. God takes what is human in the incarnation and makes it his own; the process of the incarnation is not started with the yes of Mary, but with the history of creation – God slowly incarnated himself, taking in the human condition, taking in what humanity offered and giving a conditional yes to it if he can use it to represent his incarnation. It is not because he always wanted what humanity gave, but he liked that humanity sought to give to him – sought to make itself one with him, and through that self-giving of humanity, perfectly manifested in Mary, God became man and the whole of creation was given a mediator who could properly render it to God, not through nihilistic destruction (as the way of the past), but in transformation, where what is good and true can be given eternal life.
 St. Caesarius of Arles, Sermon 84, in St. Caesarius of Arles: Sermons 81 – 186. Trans. Sister Mary Magdeleine Mueller, O.S.F. (Washington, DC: CUA Press, 1964). 18.
 Origen, Homilies on Leviticus. Trans. Gary Wayne Barkley (Washington, DC: CUA Press, 1990), 48. Origen continues with other ways our actions can be seen prefigured in the sacrifices of the Law, showing in the end, that the Christian has as much access to grace as the Law, and that we should not feel as if the Law had more ways to deal with sin.
 Hugh of St. Victor, On the Sacraments of the Christian Faith. Trans. Roy J. Deferrari (Cambridge: The Medievael Academy of America, 1951), 182.