GODFREY: He regenerated people in the Old Testament just the same as in the New.
MOHLER: As the writer of the book of Hebrews ends chapter eleven, it was meant by God that they not be saved apart from us any other way than we are.
Abraham believed, and it was accounted unto him as righteousness. How did Abraham believe? Is it because he had some kind of inherent righteousness? No. We have to believe the Holy Spirit in regeneration is the sole explanation for why Abraham believed, and it was accounted unto him for righteousness.
And I do believe that the writer of the book of Hebrews is inspired by the Holy Spirit to make that point, which is made elsewhere in Scripture, but just emphatically, just to keep in mind: there is one salvation. It works one way.