“Jude, a bondservant of Jesus Christ, and brother of James, to those who are called, sanctified by God the Father, and preserved in Jesus Christ: Mercy, peace, and love be multiplied to you. Beloved, while I was very diligent to write to you concerning our common salvation, I found it necessary to write to you exhorting you to contend earnestly for the faith which was once for all delivered to the saints” (Jude 1-3).
The “faith”, not “faiths” identifies the unique singularity of THE faith.
Unlike the plurality of false and contradictory teachings generated by evil (i.e. “the doctrines of demons”—1 Timothy 4:1), the Godhead of the one Father, one Lord, and one Spirit only produces one faith (Ephesians 4:4-6).
Though there are many faiths in this world, THE faith is the one body of doctrine revealed from heaven that bound and loosed on earth what had already been bound and loosed by God (Matthew 16:19). Nothing else contains the common salvation.