Freely received

Before Jesus sent his twelve disciples out into the villages, he gave them four short instructions: heal, raise, cleanse, set free. Straight after that he mentions the price: there isn't one. They were not to take gold or silver, and not to ask for money for what they themselves had simply been given.

The same idea is found in Jewish tradition. The Mishnah, an ancient collection of Jewish teachings, says: don't use the Torah, God's teaching, as a spade to dig with. Grace that you sell on is no longer grace. What you got for free, you pass on for free.