One thing that God ever does and never misses is self sufficiency.
The church or the congregation of God as of Old was born a self sufficient organism. Its dynamism with age and within change of covenants and orders further ascertains that. Meaning originally it was designed to be able to build its self; run its self and be self sufficient in all these things. Yet upon it all it was built to be able to be a refuge to the faring stranger, the widow and the fatherless; not just a refuge from the physical storms but also in providence spiritually and naturally as much as physically.
As there was a way to provide for the widow and the fatherless among Israel, there was a way to provide for the lay man and a way to provide for the Priest and this pattern rallies from Adam and Eve to now. Where there is a need for personnel and where there is a need for change; God did in advance work a way. So, the dues and first things were set and enforced to make the church personnel self sufficient in their pursuit to separate themselves to serving God. And this little book is about earning this self sufficiency and maintaining it. So, that the poor of the Lord and His servants may not seen begging for bread.
Psalms 37:25 KJV I have been young, and now am old; yet have I not seen the righteous forsaken, nor his seed begging bread.
The principle of dues; one of the just simply done of ethics.