Much controversy exists over the nature of the first day of the week.
Some, assuming they have come into a sphere of supposed great spiritual liberty, take it upon themselves to diminish the significance of the first day of the week. Let every man be fully persuaded in his own mind. The point of this passage is that God provides for the conscience of His children, making no allowance for it to be ignored. Believers are encouraged to seek full persuasion concerning their perspective, not allowing it to become a hollow and meaningless position. It lacks the maturity available in Christ.