What is the basic rule of first mention in Bible study?

Les explains that he follows this basic rule of Bible study by always going to the place of first mention. In practice, when a word or idea appears in the Old Testament and the same words appear in the New, he checks whether they tie together. He applies this to the phrase 'every man's sword against his brother' and compares it with Revelation 6:4, where power is given to take peace from the earth so that combatants kill one another—not the enemy but each other. He says this is unique about the great invasion of Israel. He also flips back to Ezekiel to compare the words, noting the Sovereign God will fight this battle on the hills of Israel. As an earlier illustration, he recalls Samaria being encircled and under siege, starving, until the Lord promised food by the next night; the Syrian army was suddenly routed because in their confusion they were killing each other. So it had happened before. Les adds he does not get dogmatic; if someone cannot see it, that is fine, and he would not teach it unless comfortable with it.