Yourselves is emphatic. Instead of putting Christ to the test, test yourselves. Rev., try, is better than examine. Examination does not necessarily imply a practical test. It may be merely from curiosity. Trial implies a definite intent to ascertain their spiritual condition.
The faith
See on Act 6:7. In a believing attitude toward Christ.
Prove (δοκιμάζετε)
As the result of trying.
Or know ye not, etc.
Assuming that you thus prove yourselves, does not this test show you that Christ is in you as the result of your faith in him?
Reprobates (ἀδόκιμοι)
An unfortunate translation. A reprobate is one abandoned to perdition. The word is kindred to the verb prove (δοκιμάζετε), and means disapproved on trial. See on Rom 1:28.