Did Jesus Christ observe the 1st day of the week, Sunday, as His day of worship? Did the Apostles and their converts in the 1st Century AD assemble together on a Sunday for worship services?
The answer to those questions is a resounding NO. Jesus Christ said He came to fulfil, that is to keep, the Law, not do away with it and He knew very well that the Fourth Commandment of the Law enjoined upon Him and all men to keep the Seventh Day, the Sabbath, holy as God had made it Holy Time at creation. He knew that Moses had been given the Ten Commandments, not because they war new laws at that time but that captive Israel had forgotten them.
So how did it come about that not long after the passing of the Apostles and their faithful converts that ‘christianity’ commenced to keep Sunday. Indeed there has always been christian Sabbath keepers but since very early times, small i number and heavily persecuted by a great universal church that adopted the name christian, adopted a form of ‘christian’ worship, but soon introduced easter (ishtar, astarte, ashteroth) for the Passover (or Lord’s Supper), Christmas instead of Tabernacles, and Sunday for Saturday – or the Sabbath.
Hers is a program that explains how it happened and offering written and audio materials for study. The GTA sermon offered can be found on this site.