We read in Lev 10:8-10 (NRSVCE):
And the Lord spoke to Aaron: Drink no wine or strong drink, neither you nor your sons, when you enter the tent of meeting, that you may not die; it is a statute forever throughout your generations. You are to distinguish between the holy and the common, and between the unclean and the clean
We see the Lord categorizing the objects to be used for worship into holy/common and clean/unclean. The definitive instructions were preceded by the punishment imposed on Aaron's sons for violating them:
Now Aaron's sons, Nadab and Abihu, each took his censer, put fire in it, and laid incense on it; and they offered unholy fire before the Lord, such as he had not commanded them. And fire came out from the presence of the Lord and consumed them, and they died before the Lord (Lev 10:1-2)
Now, see St Paul writing to Corinthians in 1 Cor 7:14:
For the unbelieving husband is made holy through his wife, and the unbelieving wife is made holy through her husband. Otherwise, your children would be unclean, but as it is, they are holy.
Read with Lev 10, St Paul's mention of referring to 'unclean children' appears out of place. Is it that the Church considered children born out of marriages between two non-believers, as unclean? Going by Lev 10, they could at the most be called 'not-yet-holy'.
My question therefore is: What is the significance of St Paul referring to 'unclean children' in 1 Cor 7:14 vis a vis God's instructions in Lev 10:8-10? Inputs from any denominations are welcome.