Jamieson, Fausset & Brown

The Greek order is, "For the things done in secret by them, it is a shame even to speak of." The "for" gives his reason for "not naming" (compare Eph 5:3) in detail the works of darkness, whereas he describes definitely (Eph 5:9) "the fruit of the light" [BENGEL]. "Speak of," I think, is used here as "speaking of without reproving," in contrast to "even reprove them." Thus the "for" expresses this, Reprove them, for to speak of them without reproving them, is a shame (Eph 5:3). Thus "works of darkness" answers to "things done in secret."