“The LORD has driven out before you great and powerful nations; to this day no one has been able to withstand you. One of you routs a thousand, because the LORD your God fights for you, just as he promised. So be very careful to love the LORD your God. “But if you turn away and ally yourselves with the survivors of these nations that remain among you and if you intermarry with them and associate with them, then you may be sure that the LORD your God will no longer drive out these nations before you. Instead, they will become snares and traps for you, whips on your backs and thorns in your eyes, until you perish from this good land, which the LORD your God has given you. – Joshua 23:9-13
Adolph Harstad writes:
God’s people in every era love Him and hold fast to Him only because of His love and saving actions for them, according to His plan of salvation conceived even before the foundation of the world. The writer direct God’s sharp, warning words of Law in Joshua 23:12-13 following the sweet words of grace in 23:9-11. Joshua knows the potential disaster brewing because of the nature of the heathen nations that remain – and the nature of the old Adam in every member of God’s Israel. On this side of eternity, the evil alliance of our sinful nature, the unbelieving world, and the ancient foe will always continue to assail God’s people even while they now reside in the Promised Land. Believers still need the Law to expose sin and warn of consequences, to curb their sinful nature, and to teach and guide their Christian life of God-pleasing behavior.
Joshua, the former spy who had walked the plains and thickets of the Promised Land, uses a thick cluster of metaphors drawn from hunting, exploring, and military exploits: “trapping net,” snare,” whip,” and “thorns”! That is what the Canaanites will be if Israel chooses to turn away from the LORD, compromise the faith to make peace with the unbelieving world, and keep close company with Canaanites. The heaped-up figures of speech picture the heaped-up oppression and misery. The Canaanite woman, whose body entices the eye of an Israelite as she dances at one of Baal’s fertility rites, will be a blinding thorn in the eye if taken as a bride. The image of Joshua points back to earlier warnings of the LORD. … Intermarriage with unbelievers is perilous because the unbelieving spouse will seduce the believer into apostasy and perdition, according to Deuteronomy 7:4.
The NT says much the same thing. Christians are free to marry “in the LORD” (1 Corinthians 7:39) or to take a “sister-wife” (1 Corinthians 9:5), that is, to marry a fellow Christian. If a person is brought to faith in Christ and is already married to an unbeliever, the Christian must not seek a divorce for that reason, but if the unbelieving spouse refuses to leave peaceably or deserts, then the Christian is no longer bound (1 Corinthians 7:10-16). The apostle’s exhortation for Christians in general is especially relevant for marriage:
Do not be unequally yoked with unbelievers; for what partnership does righteousness have with lawlessness? Or what communion is there for light with darkness? (2 Corinthians 6:14)
MEMORY WORK – Shorter Catechism Q/A 63
Q. 63. Which is the fifth commandment?
A. The fifth commandment is, Honor thy father and thy mother; that thy days may be long upon the land which the Lord thy God giveth thee.