Jamieson, Fausset and Brown on Acts 4:13-17

13-17. perceived that they were unlearned and ignorant men--that is, uninstructed in the learning of the Jewish schools, and of the common sort; men in private life, untrained to teaching.

took knowledge of them that they had been with Jesus--recognized them as having been in His company; remembering possibly, that they had seen them with Him [Meyer, Bloomfield, Alford]; but, more probably, perceiving in their whole bearing what identified them with Jesus: that is, "We thought we had got rid of Him; but lo! He reappears in these men, and all that troubled us in the Nazarene Himself has yet to be put down in these His disciples." What a testimony to these primitive witnesses! Would that the same could be said of their successors!