Question: "What does it mean that a biblical passage is descriptive rather than prescriptive?"
Answer: When studying the Bible, it is important to determine whether the verse or passage at hand is descriptive or prescriptive. The difference is this: a passage is descriptive if it is simply describing something that happened, while a passage is prescriptive if it is specifically teaching that something should happen. Simply put, is it a description or a command? Is the passage describing something (it happened) or is it prescribing something (it should happen)? The difference is important. When a biblical passage is only describing something but is interpreted as prescribing something, it can lead to errant thinking and behavior.
Take the story of David and Goliath, for example. Goliath was blaspheming the God of Israel and mocking God’s people, and David fought him with a sling and a stone, killed him, and cut off his head (1 Samuel 17). If we take this passage as descriptive (which it is), then there are many things we can learn from the history, such as the value of trusting God. However, if we take 1 Samuel 17 as prescriptive (which it’s not), then we might make the error of slinging rocks at blasphemers everywhere. The Bible relates the account of David’s victory for our edification, but the Bible never commands us to follow his actions on the battlefield.
A less dramatic example of the descriptive vs. prescriptive issue concerns how the New Testament describes the early Christians meeting in homes (Acts 2:46; 20:20; Romans 16:5; 1 Corinthians 16:19; Colossians 4:15). Some interpret this to mean that Christians today should only meet in homes, and, therefore, meeting in church buildings is wrong. This is errant thinking. None of the passages that describe believers meeting at home prescribe that believers only meet in homes. In fact, the New Testament nowhere instructs believers to meet in homes. The Bible describes believers meeting in homes, but there is no command to do so. So, meeting in homes is allowable, but it is not advocated or even necessarily preferred.
Another example of the importance of descriptive vs. prescriptive passages concerns the question of how often communion should be observed. From Scripture, it appears that the early Christians observed the Lord’s Supper weekly (Acts 2:42; 20:7; 1 Corinthians 11:20–25). Yet none of the passages that describe the Lord’s Supper being observed weekly actually prescribe that it be observed weekly. Can the Lord’s Supper be observed weekly? Absolutely. Must the Lord’s Supper be observed weekly? No.
The gift of tongues is another area in which it is important to separate descriptive from prescriptive passages. The book of Acts gives us several instances of people speaking in tongues, such as Acts 2:4, “All of them were filled with the Holy Spirit and began to speak in other tongues as the Spirit enabled them.” Some take this and other passages describing tongues and assume they are prescriptive, but this is a wrong interpretation. The Bible describes certain occasions when Spirit-filled people spoke in tongues, but the descriptions of what happened should not be confused with commands to make it happen. The Bible certainly commands us to be filled with the Spirit (Ephesians 5:18), but nowhere does it say that speaking in tongues always accompanies the filling, and neither does it mandate speaking in tongues for anyone.
As a general rule, much of what occurs in the book of Acts is descriptive, while much of what is said in the New Testament Epistles is prescriptive. Acts is history, and the Epistles are instruction. There are exceptions, of course. The book of Acts sometimes prescribes, and the Epistles sometimes describe.
If a verse or passage is simply describing something, with nothing said in the positive or negative about that something, then it is descriptive and should not be considered something we are commanded to do. It is only when Scripture specifically instructs (prescribes) that New Testament believers do something that we are to take it as a command to obey.