Was the Sabbath changed from the seventh day of the week to the first day? Well, yes and no. Let’s deal with the “no” first.
God, “with whom there is no variation or shadow of turning” (James 1:17), does not change (Malachi 3:6). The Israelites received two laws from Moses: the law of Moses, that of ordinances and ceremonies; and the Law of God, embodied in the Ten Commandments, which is an expression of God’s character. If God does not change, neither will His Law. “My covenant I will not break, nor alter the word that has gone out of My lips” (Psalm 89:34). “I know that everything God does will endure forever; nothing can be added to it and nothing taken from it” (Ecclesiastes 3:14). “The works of his hands are faithful and just; all his precepts are trustworthy. They are steadfast for ever and ever, done in faithfulness and uprightness” (Psalm 111:7, 8).