Receive not an accusation (κατηγορίαν μὴ παραδέχου)
Neither word in Paul. For accusation see on Joh 5:45. It means a formal accusation before a tribunal. The compound verb παρὰ emphasizes the giver or transmitter of the thing received: to receive from another.
But (ἐκτὸς εἰ μὴ)
Except. A pleonastic formula, except in case. The formula in 1Co 14:5; 1Co 15:9.
Before (ἐπὶ)
Or on the authority of. On condition that two witnesses testify. The O.T. law on this point in Deu 19:15. Comp. Mat 18:16; Joh 8:17; 2Co 13:1.