According to Romans 15:4, why were the Old Testament things written down?
The Old Testament things were written for our learning, as Paul states in Romans 15:4. All these things are written back in the Old Testament for our learning, and we are to learn from them. The record of God's separation of Israel from Egypt teaches that God likewise separates the believer from the world.
Les explains that Paul, in Romans 15:4, says all these Old Testament things were written for our learning, and we are to learn from them. He then points to a New Testament analogy in 2 Corinthians 6, where Paul gives the same set of directions. Just as God put a division between Israel and Egypt—drawing an invisible line around Goshen so that even the insects would not cross—God now puts a line of demarcation between the believer and the world. God says you cannot serve two masters; you will serve one and hate the other. The Old Testament record teaches that believers are to be set apart, just as Israel was to be a set-apart, covenant people who had nothing to do with the pagan Gentiles around them.
For whatsoever things were written aforetime were written for our learning, that we through patience and comfort of the scriptures might have hope.