In Matthew 19, Jesus establishes the basis for a celibate clergy and the renunciation of worldly wealth by the monks and nuns of Christianity.
Not everyone wants to, or is able to, become a monk or nun.
But those who hear such a calling, should be supported by the laity for it is only those who meditate upon God who are able to answer questions about God.
So, offering food to the monks, returns many rewards to the laity, rewards not earnable in any other way.