Chapter 19 begins with the Lord calling the people to come to the base of Mount Sinai. They were told to approach the mountain at a certain time and to remain at the base of the mountain. There was smoke and fire, lightning and thunder. Then God calls Moses to approach and would respond to Moses through thunder. The text of Exodus doesn’t indicate if there was words that possibly boomed like thunder, or maybe the voice of the infinite God was too mighty and powerful for the people to comprehend with their finite minds. Either way, after they receive the Ten Commandments they say it was all too much for them, and they begged Moses to be their spokesperson and intercessor on their behalf because they couldn’t bear to hear that booming of thunder again.
In chapter 20 we hear the Ten Commandments proclaimed by God. These commandments, called the Decalogue in the catechism (meaning “Ten Words”), are the foundation of the moral law and are in force even today. What that means is that breaking one of the commandments is grave matter, even in the New Covenant, because what is contained in them are based on natural law and can never be abrogated or dispensed from.
For example, worshiping another god is never permissible, for any reason or at any time, while the obligation to fast on certain days can be dispensed by the Church for various reasons (pregnancy, infirmity or old age being common ones). What is contained in the Decalogue is eternal, binding, and indispensable to us.
While many of the laws and regulations of the Old Testament are no longer applicable to Christians, the Ten Commandments remain because the moral law remains. Jesus sums up the “whole of the law” in the Gospels by saying we should love God and neighbor. This is because the first three commandments direct us towards love of God, and the last seven direct us to loving relationships with our fellow man. If we love both, we’d never transgress any of the commandments.
For more on the Ten Commandments see https://www.catholic.com/magazine/print-edition/why-we-are-not-bound-by-everything-in-the-old-law
Jesus transitions into this parable of the wise and foolish virgins from his speaking on the destruction of Jerusalem and the end of the world in the previous chapter.
The moral of this parable is three fold; in the immediate term, Jesus is warning the disciples to be vigilant for the signs that he just laid out to them, for when this coming judgment would happen, and when it does they should head for the hills. And that is exactly what Eusebius says Christians I’m Jerusalem did during the siege of the city.
In the long term, this parable also means to watch for the second coming of Christ, when the world will draw to a close and God will judge the nations and inaugurate the world to come.
Then on a personal level, the waiting for the bridegroom signifies the uncertainty of the length of one’s life. The bridegroom (Jesus) may come for you to call you home in childhood, in young adulthood or when you are old and frail, but we know that day is certain and it’s coming for us all. So we need to keep the flame of Christ, that we receive in the baptismal liturgy, alive in our hearts and be ready for that moment.
Jesus then moves into telling the parable of the talents. The meaning of this parable is that the gifts and abilities we are given are not for our exclusive benefit. Just like the servants aren’t handed the talents just for them, but they are supposed to use them to increase them and then return them to the master. We are not saved from our sins alone or just for our own sake, but we are incorporated into the Body of Christ. As members of the body we have to pull our weight and carry out whatever function God has in store for us. That is why some early Christians believed the lamps represented our Christian lives and faith (time from baptism until death) and the oil represented spiritual and corporal works of mercy, like the ones Jesus described at the end of this chapter. So we keep our faith (the lamps) alive through these good works, remembering that we aren’t saved by works, but that also as Saint James says, faith without works is dead. Just like a lamp without oil.