Q. 1. Why are priests paid a salary. Since they are serving God, should they not be doing so for free? Matthew 10:8 says, "Freely you have received; freely give."
A. 1. In Matthew 10:9-10, Jesus said, “Do not get any gold or silver or copper to take with you in your belts — no bag for the journey or extra shirt or sandals or a staff, for the worker is worth his keep." This instruction amounted to trust in Divine Providence. Take nothing with you - trust in the Lord to provide your needs.
The Apostles received freely from Jesus the Good News. Accordingly, they were expected to share freely the Good News with the lost sheep of Israel. In doing so, they should expect the Israelites to welcome them in their homes and provide their basic needs of shelter, food, clean clothing, etc...
In those days, the priests could survive on the basic necessities. Nowadays, things are different. The priest must have a shelter. Who will pay the rent? Or will someone take in a priest on a permanent basis, feed him, provide him with all his needs, medication, transportation, etc...
Saint Paul tells us, "In the same way, the Lord has commanded that those who preach the Gospel should receive their living from the Gospel." [1 Cor. 9:14] In other words, the priests should receive a salary for their ministry.
In Romans 15:26-27, we read that those who receive the Good News, they should share their spiritual blessings with the priests:
"For Macedonia and Achaia were pleased to make a contribution for the poor among the Lord’s people in Jerusalem. They were pleased to do it, and indeed they owe it to them. For if the Gentiles have shared in the Jews’ spiritual blessings, they owe it to the Jews to share with them their material blessings."