John Trapp on Proverbs 31:8

Verſ. 8. Open thy mouth for the dumb] i.e. Speak wiſely and freely for thoſe that either cannot, or may not ſpeak for themſelves. Thus Nicodemus ſpoke for our Saviour, Joh. 7.51. Paphnutius in the Council for the married Clergy, Pliny to Trajan for the perſecuted Chriſtians, the Elector of Saxony for Luther, &c. Oecolampadius ſaith, that wiſe men only open their mouthes, for a fools mouth is never but open. Oecolamp. in Job 33. Hence [non-Latin text not transcribed] Gapers are put for fools in Lucian and Ariſtophanes.