Sex before marriage: Paul in 1 Corinthians 7:2 — the solution to sexual immorality is marriage, which means sex outside marriage IS sexual immorality. If premarital sex were acceptable, marriage wouldn't be needed to avoid sexual immorality. Marrying outside the faith: 1 Corinthians 7:39 — free to remarry "only in the Lord." 2 Corinthians 6:14 — unequally yoked.

1 Corinthians 7:2: because of sexual immorality, each should have their own spouse. If premarital sex were OK, this instruction is pointless. The cultural normalization of sex outside marriage through media doesn't change Scripture. 1 Corinthians 7:39: remarriage is permitted "only in the Lord" — restricting to fellow believers. Mixed marriages (1 Cor 7 earlier) create significant problems.