A shepherd in the wild would build a sheepfold. This was a pen with low stone walls topped by sharp branches, to keep his sheep safe at night.
The pen had one gate (or opening in the wall) that was closed with branches. Any person or thing that came into the pen threatened the flock.
A bad shepherd was like a thief and a robber. He used the sheep for his own gain and did not care for them. Bad shepherds took the sheep’s milk and wool for themselves. They killed the sheep without guaranteeing their safety (Ezekiel 34:3; see Isaiah 56:11; Jeremiah 23:1–4).
These words were the strongest rebuke Jesus spoke against the Jewish leaders.