A.T. Robertson Commentary Mark 4:33

"And with many such parables spake he the word unto them, as they were able to hear it;" — Mark 4:33 (ASV)

As they were able to hear it (καθως ηδυναντο ακουειν). Only in Mark. Imperfect indicative. See Joh 16:12 for ου δυνασθε βασταζειν, not able to bear. Jesus used parables now largely, but there was a limit even to the use of them to these men. He gave them the mystery of the kingdom in this veiled parabolic form which was the only feasible form at this stage. But even so they did not understand what they heard.