Augustine of Hippo — as excerpted in the Catena Aurea on John 18:19-21

“(Tr. cxiii) There is a difficulty here not to be passed over: if He did not speak openly even to His disciples, but only promised that He would do so at some time, how was it that He spoke openly to the world? He spoke more openly to His disciples afterwards, when they had withdrawn from the crowd; for He then explained His parables, the meaning of which He concealed from the others. When He says then, I spake openly to the world, He must be understood to mean, within the hearing of many. So in one sense He spoke openly, i. e. in that many heard Him; in another sense not openly, i. e. in that they did not understand Him. His speaking apart with His disciples was not speaking in secret; for how could He speak in secret before the multitude, especially when that small number of His disciples were to make known what He said to a much larger?”