John Calvin Commentary Romans 3:10

"as it is written, There is none righteous, no, not one;" — Romans 3:10 (ASV)

As it is written, etc. He has until now used proofs or arguments to convince people of their iniquity; he now begins to reason from authority. For Christians, this is the strongest kind of proof when authority is derived from the only true God. Therefore, let ecclesiastical teachers learn what their office is; for since Paul asserts no truth here except what he confirms by the sure testimony of Scripture, much less should such a thing be attempted by those who have no other commission than to preach the gospel, which they have received through Paul and others.

There is none righteous, etc. The Apostle, who gives the meaning rather than the entire words, seems first, before he comes to particulars, to state generally the substance of what the Prophet declares to be in humankind. And that is—that none is righteous. Afterward, he particularly enumerates the effects or fruits of this unrighteousness.