How did the Rabbi interpret the sign over gate leading into the camp?

From the text:

A wrought iron gate stood in front of the buildings, and over the gate was a sign proclaiming in large black letters: ARBEIT MACHT FREI. Several of the villagers whispered the words, but the rabbi, his hand up to his eyes, strained to read them.
"What does it say, Faygeleh?" he asked, clinging to his daughter's hand, suddenly an old man. "My eyes . . ."
But Fayge was beyond answering. It was Hannah who told him, her voice bitter. "Work makes you free," she said.
The rabbi nodded. "See, my children," he said hoarsely, "we are in God's hands. We are not afraid of work."