What about the situation, though, where one of the parents is a “believer,” a Christian, but the other is not? Does this union, or a continuation of the union without separation, make the believer contaminated or unclean, making the children unclean as a consequence?

No. Why not? Because of the righteous principles of God, by which he stands loyally, and because of his loving-kindness toward those who serve him with exclusive devotion. He comforts those in religiously divided households, where one is a believer and the other is not, saying in his Word: “For the unbelieving husband is sanctified in relation to his wife, and the unbelieving wife is sanctified in relation to the brother; otherwise, your children would really be unclean, but now they are holy.”​—1 Cor. 7:14.

In the Hebrew and Greek languages, in which the Bible was written, words drawn from the Hebrew word qa·dhashʹ which has the root meaning “to be bright, new, clean,” and from the Greek word haʹgi·os are rendered “holy,” “sanctified” and “set apart.” Both the Hebrew and Greek usage had a religious, spiritual and moral sense. Anything sanctified, therefore, would be clean, holy, set aside for God’s service.

This clean standing before God comes by the exercise of faith in God’s provision through his Son. One not exercising this faith has not been cleaned up from his inherited imperfection, sinfulness. Such persons, termed by the apostle Paul as ‘unbelievers,’ may be living honest, moral lives. But they have not separated themselves from the unclean world. They have not accepted God’s provision for removal of their sinful state, not yet having been set free from slavery to sin by becoming true followers of the Lord Jesus Christ. Such persons are not, of themselves, clean in God’s eyes.​—2 Cor. 6:17; Jas. 4:4; John 8:34-36.

Note that the apostle’s statement, at 1 Corinthians 7:14, does not say that the unbeliever is, by the marriage bond, made clean or holy himself. He may, in fact, be one who carries on wrongdoing or unclean practices. Rather, Paul says the unbeliever is sanctified “in relation to” the believer. So God counts such marriage relationship or union clean, as a loving-kindness to the believer and the young children.

On what basis can God thus favor the young children of religiously divided families? Well, marriage is an institution of God, and the marriage relationship is a proper arrangement for humans. Therefore, any proper marriage has God’s approval. He counts the marriage partners as “one flesh.” (Matt. 19:5) Accordingly, when one of the partners is a faithful Christian, that one is not contaminated by continuing to live with the unbelieving one. The marriage is acceptable to God. If it were not acceptable, the children would be like illegitimates. But now they are counted as holy, clean. Or, if both the partners are unbelievers, the marriage itself is not condemned, but the children are counted like their parents, not sanctified or holy to God.

What does having the merit of a Christian parent or parents mean to the obedient child? It means that he has the favor of God. He has God’s protection and help, just as his Christian parent does. He does not have the judgment of God against him, as does the world. (2 Pet. 2:9; compare Psalm 37:25, 26.) When God executes judgment on the wicked he will spare such children as being clean, holy, just as the believing parent is holy.

Conversely, the Bible declares: “‘For, look! the day is coming that is burning like the furnace, and all the presumptuous ones and all those doing wickedness must become as stubble. And the day that is coming will certainly devour them,’ Jehovah of armies has said, ‘so that it will not leave to them either root or bough.”’ (Mal. 4:1) When Jerusalem was destroyed in 70 C.E. because of its unfaithfulness to God, children were killed along with their parents. Christians who had heeded Jesus’ prophetic warning to get out of the doomed city before the Romans sealed it off were saved along with their children.

Likewise at the destruction of the wicked in this present system of things the principle will apply: The offspring (the bough) not taking a righteous stand on their own will receive the same adverse judgment as the parents (the root).