Sabbath vs Sunday

The last day of the week to honor got changed to the first day of the week.
[Acts 20:7] And upon the first day of the week, when the disciples came together to break bread, Paul preached unto them, ready to depart on the morrow; and continued his speech until midnight.
Upon the first day of the week, when the disciples came together - This, compared with 1 Cor. 16:2, and other similar allusions, plainly indicates that the Christian observance of the day after the Sabbath, ‘Sunday’ was already a fixed practice of the churches. The Gentile believers changed to Sunday, G-d did not.
Since the Hebrews honored G-d’s Sabbath, the Gentiles choose to honor Sunday.
Since the Hebrews honored G-d’s Passover, the Gentiles choose to honor Easter.
Y’Shua, Himself honored the Fathers set Festivals, I do not understand how Gentiles can justify changing G-d’s plans, though it is now a tradition that no one questions.
And no one chooses to return to G-d’s original plan.