Immorality leads to impurity.

The acts of the flesh are obvious: sexual immorality, impurity, and debauchery. Galatians 5:19

The sinful desire of the flesh leads to uncleanness, sexual immorality, and sensuality.

THAT you abstain from things offered to idols, from blood, from things strangled, and sexual immorality. If you keep yourselves, from these you do well." Acts 15:29

Sexual immorality is an impure act.

How could be be sanctified? By avoiding sexual immorality.