Everyone has common faith. If you believe the sun will rise tomorrow morning, that is because you have common faith. Many ministers think common faith and saving faith are just different degrees of the same thing. This error was promoted in American salvation theology by Scottish Common Sense Realism. Here's the heresy in John Witherspoon's words:

FALSE PREMISE 1: There is no difference between common and saving grace.
Witherspoon wrote: “There were … great debates whether special and common grace differ essentially in their nature, or if they differ only in degree… I embrace the last of these opinions”.

FALSE PREMISE 2: There is no difference between common and saving faith.
Witherspoon wrote: “What is faith? Is it any more than receiving the record which God hath given of his Son, believing the testimony of the Amen, the true and faithful Witness?”

When modern ministers call common faith in God apart from regeneration, they ignore James' warning, "Thou believest that there is one God; thou doest well: the devils also believe, and tremble" (James 2:19). They forget, or ignore the Apostle Paul's clear delineation of saving faith as a gift of God from saving grace. "For by grace are ye saved through faith; and that not of yourselves: it is the gift of God: Not of works, lest any man should boast" (Ephesians 2:8-9).

Saving faith is a gift of God given ONLY when He causes supernatural regeneration. This distinguishes it from common faith. If someone has common faith in Christ, or what some call "bare faith" in Christ, this is NOT saving faith, since it is not concomitant or consecutional to supernatural regeneration.

Only at supernatural regeneration can a person have saving faith.

Saving faith is the instrument of salvation. Unless the person is supernaturally regenerated by God, that instrument of salvation DOES NOT EXIST. In other words, the orthodox view is that faith is granted to the individual and contributes nothing to salvation but is merely the instrument whereby the person lays hold of Christ's righteousness.