How did this change in observance of days come about, suddenly or gradually?

Answer

Gradually.
NOTES - "The Christian church made no formal, but a gradual and almost unconscious
transference of the one day to the other." 'The Voice From Sinai," by Archdeacon W. F. Farrar page 167.
This of itself is evidence that there was no divine command for the change of the Sabbath.

What witness does the true believer in Christ have that he is accepted of God?
In all we do, whose glory should we have in view?
What was indicated by the mixture of clay and iron in the feet and toes of the image?
In what was shown the first tangible evidence of this \"falling away\" from the truth of God?
12. Are men's hearts now \"failing them for fear, and for looking after those things which are coming on the earth\"?
What will he one of the last great signs performed by this means, to fasten men in deception?
For what purpose was the earth created?

Questions & Answers are from the book Bible Readings for the Home Circle