We tend to take for granted that the sermon was given on a mountain because we know that Jesus frequently climbed mountains (Luke 6:12, John 6:15, etc.) – though he usually did this to get away from people, to be alone and to pray. In this case we are told he specifically went up on a mountain with his disciples following him.
The New International Version tells us “Now when Jesus saw the crowds, he went up on a mountainside and sat down. His disciples came to him, and he began to teach them” (Matthew 5:1-2). This gives the impression that Jesus simply went up on the side of a mountain – the lower slopes. But “side” is not in the original Greek (or in most translations), and the Greek anebē eis to oros “he went up into a mountain” conveys the sense that he ascended on to the mountain – certainly well up toward, or to, its summit.
Now this wording is interesting, because when we compare it with the Old Testament account of how Moses went up onto Mt. Sinai to receive the law from God, we find “When Moses went up on the mountain …” (Exodus 19:3, 24:12). In fact, the Septuagint, the Greek translation of the Hebrew Scriptures which many of the writers of the New Testament used, translates this with exactly the same words as those used of Jesus ascending the mountain: anebē eis to oros.
Many Jewish readers of the 1st century would have recognized the beginning of this story of the Sermon on the Mount as being identical to the beginning of the story of Moses receiving God’s law. This would have struck a deep chord for those readers because every devout Jew knew that God had told Moses: “I will raise up for them a prophet like you from among their fellow Israelites, and I will put my words in his mouth. He will tell them everything I command him” (Deuteronomy 18:18). Every devout Jew expected this prophet like Moses, and the similarities between Jesus and Moses were clear for those ancient readers who knew the Hebrew Scriptures.
For example, the infant Moses and Jesus both escaped death when a ruler attempted to kill the male Jewish children in the area, both hid in Egypt as a child, both gave up life in a kingly home to lead a humble life of service, both fasted forty days and nights, both communicated directly with God, both performed miracles, both provided the people with bread to eat, both sent out 12 individuals, both chose 70 individuals, both taught with authority – and both ascended a mountain for the giving of key commands and instruction from God.
With that background in mind, we can see the significance of the fact that throughout the first third of the Sermon on the Mount the law of Moses is mentioned repeatedly, using the formula “You have heard that it was said to the people long ago …. But I tell you ….” For example:
“You have heard that it was said to the people long ago ‘You shall not murder, and anyone who murders will be subject to judgment.’ But I tell you that anyone who is angry with a brother or sister will be subject to judgment” (Matthew 5:21-22, and see also Matthew 5:27, 31, 38, 43).
Within the Sermon on the Mount, Jesus made it clear to his followers that he was not doing away with or replacing the principles of the law given through Moses (Matthew 5:17-19). Instead, in this pivotal sermon – the longest connected teaching of Jesus in the New Testament – he gave new insight into God’s spiritual laws, raising our understanding of their intent to the higher level to which we are called.