This particular point of obedience is especially interesting because it is the first thing mentioned about our faithfulness to Him. This passage bans Israel from making covenants with the people of the land. Among covenants are marriage unions. A marriage is a covenant to be special treasures to each other and therefore faithful to each other. As we continue in the chapter, verses 4 and 6 begin with the conjunction "for," which tells us why something is to be done or is forbidden.
Here, unlike some other situations, He provides a brief reason or two why this is forbidden. In short, in verse 4, covenants—including marriages with the heathen—are banned because it is too spiritually dangerous. It is similar to playing with fire—the Lake of Fire. Interreligious marriages will work to destroy the special faithfulness to each other.
In verse 6, God's reason is that they—and we—are a special, set apart people for God's uses only. Entering covenants with the heathen, including marriage and honoring their gods, will work to destroy the special relationship. In other words, it will work to destroy our faithfulness to God and therefore our ability to proclaim God's praises.
Do we love God enough that we are willing to heed His commands, or do we love ourselves more than Him, making us willing to risk what He says not to do? Marrying outside the faith is a matter of idolatry.
The perspective through which we look at these things in the course of daily life makes all the difference in the world. A common way of illustrating this is to ask whether we consider the glass half-full or half-empty. Do we think of God's calling as a blessing that has opened a door to a fabulous eternity? Or, do we feel it bars us from areas of fulfillment, excitement, adventure, and fun in life, excluding us from those who have access to all the pleasure and glory this world can produce?