Matthew 10:8-Heal the sick, raise the dead, cleanse lepers, cast out demons. You received without paying; give without pay. 
The thought of being payed according to “our work” is such a natural cycle of our society and world, that it can be difficult to think we can receive anything of great value without working for it.  The only exception I can think of is receiving a wealthy inheritance from a rich relative…
So if that were our situation, we know from a foundation standpoint we didn’t earn it, we just received it.  So we can’t be as proud as we might be with our inheritance, if we were the ones who accumulated the wealth in the first place.  It could be easier to adopt the mentality that “since I was so richly blessed without earning it, I can pass it onto others”.  Which allows for the natural inheritances to be passed on, unless someone becomes selfish and squanders it…
This is the same principle Jesus was trying to convey to His disciples after sending them out to minister.  That the grace and power they are receiving is something they didn’t earn, but was given to them freely.  So “armed” with that mentality, they should not charge or make people earn their services of ministry.  That they are to keep passing on this “rich inheritance” to others, that they can be blessed by it.
It is key that we understand the grace of God on our lives, and how rich of an inheritance we do have in Christ (Ephesians 1:11-23).  But it maybe just as important to remember how much we don’t deserve, nor have we earned God’s favor!  This helps us to remain unconditional in our service of each other and the world.  Helping them understand that they don’t have to earn God’s love, but like us to first freely receive it, and then freely give it!
In His Love, Ld