Leviticus 21:15

And if the first part of the dough is dedicated to God, the entire batch of dough will be also. And if the roots [of a tree] are dedicated to God, the branches will be also.

For the unbelieving husband is set apart [i.e., as an acceptable mate, although not yet saved. See verse 16], through his wife [i.e., her Christian commitment is viewed as having a godly effect on the home], and the unbelieving wife is set apart through the brother [i.e., for the same reason]. Otherwise, your children would be [considered] unclean. [Note: "Unclean" suggests they would be viewed as pagans were it not for one parent being a Christian]. But, as it is, they are set apart as acceptable [i.e., to God, because of the influence of the one Christian parent].