Examine yourselves, whether ye be in the faith; prove your own selves. Know ye not your own selves, how that Jesus Christ is in you, except ye be reprobates? Examine yourselves, whether ye be in the faith - Ἑαυτους πειραζετε· Try yourselves; pierce your hearts; bore yourselves throughout; try yourselves by what I have written, and see whether ye retain the true faith of the Gospel.
Prove your own selves - Ἑαυτους δοκιμαζετε· Put yourselves to the test, as you would try gold or silver suspected of adulteration. No more take that for Gospel which is not so, than you would take adulterated money for sterling coin. This is a metaphor taken from testing or assaying adulterated metals.
Know ye not your own selves - Are ye not full of wisdom and understanding? And is it not as easy to find out a spurious faith as it is to detect a base coin? There is an assay and touchstone for both. If base metal be mixed with the pure you can readily detect it; and as easily may you know that you are in the faith as you can know that base metal is mixed with the pure. Does Jesus Christ dwell in you? You have his Spirit, his power, his mind, if ye be Christians; and the Spirit of Christ bears witness with your spirit that ye are the children of God. And this is the case except ye be reprobates; αδοκιμοι, base counterfeit coin; mongrel Christians. This metaphor holds excellently here. They had a Judaizing Christian among them; such, presumptively, was the false apostle: they had received his Judaico-Christian doctrine, and were what the prophet said of some of the Israelites in his time. Reprobate silver, adulterated coin, shall men call them, Jeremiah 6:30. And thus, when they were brought to the test, they were found reprobate; that is, adulterated with this mixture of bad doctrine. There is no other kind of reprobation mentioned here than that which refers to the trial and rejection of adulterated coin; and, by way of metaphor, to the detection of false Christianity. This reprobation came of the people themselves: they, not God, adulterated the pure metal. Man pollutes himself; then God reprobates the polluted.