1 Corinthians 7:14–17
14 For the unbelieving husband is sanctified by the wife, and the unbelieving wife is sanctified by the husband; otherwise your children would be unclean, but now they are holy.
15 But if the unbeliever departs, let him depart; a brother or a sister is not under bondage in such cases. But God has called us to peace.
16 For how do you know, O wife, whether you will save your husband? Or how do you know, O husband, whether you will save your wife?
17 But as God has distributed to each one, as the Lord has called each one, so let him walk. And so I ordain in all the churches.
The word sanctified does not always have to mean saved. We need to be careful of reading into a passage, or making a passage say what we want it to say. For example, Paul uses the same word, sanctified, ἀνασῴζω hagiazo, in 1 Timothy 4:4-5, and in that context, he discusses eating meat.
A person is not saved merely by association with his or her spouse. Salvation is by grace through faith in Jesus Christ (Ephesians 2:8-9). So what does Paul mean? The passage at hand is a difficult one and deserves more study.
Since he is speaking to a Jewish audience, is he referring to some Jewish tradition? One clue that validates this proposition is his mention of children unclean, but now they are holy. That is a wholly Jewish statement; Gentiles would not have an issue with anything clean or unclean.
Even the word save (sozo) does not have to mean salvation as we understand it. The Greek word σῴζω sozo, for example can mean to be made whole. It can also mean to save one from suffering.
Is Paul saying in verse 17, while it may not be perfect, be satisfied with your current marital state?