Scripture plainly reveals that God repeatedly calls for His people to separate from the world. This separation extends to every aspect of life, especially including the marriage bond. Why? Because God knows the very real danger that unbelievers pose to believers by drawing them away from Him (Deuteronomy 7:3-4; Judges 3:6-7; 1 Kings 11:2). This is why God specifically instructed His people in both the Old and New Testament to marry among themselves (Jew with Jew and Christian with Christian). The nation of Israel was forbidden to yoke up with the surrounding nations because Israel would adopt heathen practices and the worship of false gods (Exodus 34:15-16). Though God’s commands for the New Testament believer are often different from His plan for the Jew, in this aspect they remain constant and unchangeable.
This world, though it consistently fails to recognize and know the Lord, should consistently recognize Christ's conversation through the life of the believer. Our conversation should always match, or become, the gospel of Christ and the new life that we have in Him. Our conversation should be holy because the Lord is holy (1 Peter 1:15). In 2 Peter 3:11, we learn that the dissolving of this world ought to cause us to walk “in all holy conversation and godliness.” In other words, our practical Christian life should resemble the change inside of us that took place at salvation. Others should see the Lord Jesus Christ in our actions and in our way of life.
