We live in an age deeply influenced by the philosophy of existentialism. At its core, existentialism is the conviction that people are free – radically so – to define their life, their future, and their existence. There is, arguably, a lot of good that has come from the rise of existentialism in the imagination of Western society. It has elevated the rights and freedoms of individuals. It has encouraged the culture to open more doors of opportunity to more people (especially those who had previously been excluded). And, it has encouraged people to dream, achieve, and take greater responsibility for their lives.
However, if existentialism had a bumper sticker, it would likely be the famous line from the philosopher Jean-Paul Sartre, “Existence Precedes Essence.” In those three words Sartre expresses existentialism at its extreme. From this perspective, humans do not have an essence, a goal, or a pattern to live into. Rather, humans are pure existence, and each person must define for themselves what they want to become.
The primary purpose of a hammer is to drive in nails. A hammer may be used for other purposes. It could be used as a weapon, as a door stop, or as a paper weight. However, unless it ultimately gets used to build and construct something, it does not fulfill its true purpose. For existentialism in its extreme, no such purpose or pattern exists for human beings. What is unique for humans is the radical freedom to determine one’s purpose and pattern.
In significant ways the Law or Torah resists the idea that humans are radically free to determine their own existence. The Torah proclaims that humans are actually created with an essence – the Image of God – prior to existence. Though that image may be marred and distorted, obedience to the Law not only restores, for Israel, the relationship to the Creator but also the relationship to others and to the creation.
This text, Exodus 24:12-18, contains just a slice of the great story of God’s giving of the Torah to Moses and to the people. It is a text filled with the mystery and awe of God’s glorious presence. God takes the initiative to invite Moses up the mountain (v. 12), and Moses, with his leadership heir Joshua, immediately obeys (v. 13).
The mountain is covered with the glorious presence of God. The symbols of God’s mystery (the cloud) and the symbol of God’s holiness (fire) are both at hand. Two symbolic numbers also are there in the text. Moses receives God’s revelation of the Law on the seventh day; seven being the number of completion. There is no lack or gap in the revelation of God’s purposes through Moses. Like the blessing of shalom received on the seventh day of the creation narrative, so too, through the Law, Israel will rediscover God’s shalom. Moses also stayed on the mountain for forty days. Like the rains in the days of Noah, or the years of transformation in the wilderness, forty is a number symbolizing a time of challenge and growth that is long enough that at its end transformation has happened. The Law will not be a burden to the people. It will not be easy to be faithful to Torah-living, but the Law will still be a means of grace that brings about transformation.
Of course, this text is present on Transfiguration Sunday because of its obvious connection to the Gospel text for the day, the story of Christ’s transfiguration. In the Matthew 17 text, Jesus, like Moses, goes up the mountain with those who will carry forward his ministry. The glory of God is made known through Christ, and Moses and Elijah are present.
The two texts are obvious echoes of one another. It is significant, in the light of the Exodus text, that Moses is present in the transfiguration of Jesus. In Jesus, God’s prior work through the Law and the Prophets are coming together. Jesus did not come to eliminate the Law and the Prophets but to fill them full (Matt. 5:17). Again, the inclusion of the Exodus text is a reminder that the purpose of the Law has not been set aside in the person of Jesus. It has instead been fulfilled.
There has been a tendency in some Protestant theology to believe that the purpose of the Law was simply to frustrate God’s people (apparently for generations) so they could be prepared to receive the grace of God made available through Christ Jesus. From this perspective, grace sets us free from the need to adhere to any Law. This antinomianism (or lawlessness) can end up looking at times like radical existentialism or even forms of Gnosticism. “It doesn’t matter what I do with my body or life,” this perspective might think, “because grace has set me free to do what I want and create my own essence.”
That misunderstands the purpose of the Law. The Torah was not meant as a frustrating burden on God’s people but as a way to reconnect with the purposes for which they were created. The Law may be incomplete, but its purpose was to help people rediscover the harmony that comes when people live according to God’s will. Entering into the kingdom of Jesus does not eliminate the need to live within the guardrails of creation, rather it moves the Law from tablets of stone to the flesh of our hearts.
Thus, as congregations we hear texts like Exodus 24 as an invitation to recalibrate our hearts to the purposes of God made complete on the mountain of Transfiguration. As James K.A. Smith articulates well,
The announcement of the law and the reading of God’s will for our lives represents a significant challenge to the desire for autonomy that is impressed upon us by secular liturgies… The announcement of the law reminds us that we inhabit not “nature,” but creation, fashioned by a Creator, and that there is a certain grain to the universe – grooves and tracks and norms that are part of the fabric of the world. And all of creation flourishes best when our communities and relationships run with the grain of those grooves… That is why the law, though it comes as a scandalous challenge to the modern desire for autonomy, is actually an invitation to be freed from a-teleological wandering. It is an invitation to find the good life by welcoming the boundaries of law that guide us into the grooves that constitute the grain of the universe and are conducive to flourishing. 
The mountain of the Lord does not eliminate the mountain of Moses. Indeed, Moses is still present on the mount. What the mountain of Moses began – the restoration of people to their divinely created purpose – was filled full.  James K.A. Smith, Desiring the Kingdom: Worship, Worldview, and Cultural Formation (Grand Rapids: Baker Academic, 2009), p. 176.